It's the mildest of mild winters down here in the south of Italy and, last weekend at Bácoli, a pretty suburb by the seaside west of Naples, the customers of Pizzeria "Da Enrico" were making the most of it. Neapolitan families come here on Sunday for some fresh air and greenery: the restaurant has a garden and a swimming pool, and the place was packed. Few of his customers had a clue that Enrico Mazzarella, the proprietor, 47, was a reformed gangster.

Nor did anyone pay special attention to the four young men who strolled in at 2pm, looking like ordinary customers. "Which one is Enrico Mazzarella?" one of them inquired, and when Mazzarella was pointed out ­ hard at work taking orders ­ they pulled pistols out of their pockets and shot him eight times in the head.

The placid Sunday scene ­ family groups, children, babies, old folks ­ turned within seconds into something out of Chicago in the 1930s, with terrified customers screaming and wailing, grabbing their children and hurling themselves to the ground. The killers ran off and, within minutes, all the customers had departed, too ­ long before the police showed up. Nobody in Naples fancies playing the part of witness to a Camorra killing.

Enrico Mazzarella was the 23rd victim in the past month of a Naples gangland feud more bitter and bloody than any this city has seen since the 1980s. More theatrical, too, in this melodramatic city, magnificent but catastrophic, with its grand, imperial architecture gone to seed, its alleys and high tenements.

The warriors in Naples's new war, like the thugs in the Godfather films, commit murder as chillingly and publicly as possible. One young man was blown off his motorcycle. Another was killed in a city pizzeria, his head smacking face down into the meal that had just been delivered to his table.

The most sought-after victims have vanished, fleeing the city altogether or barricading themselves into their highrise flats in the city's slums. So the killers go after collateral targets, people such as the restaurateur Enrico Mazzarella whose criminal years were far behind him. They go after people such as Gelsomina Verde, the 21-year-old woman whose only crime was to have had an affair with a gangster who had gone to ground. Gelsomina's tortured and burnt body was found two weeks ago. It is a war waged by young men as ruthless as they are stupid. Big and powerful criminal gangs make immense fortunes out of drugs such as heroin, cocaine and marijuana in many Italian cities but mostly they go about their business with very little bloodshed, because, as they say, "when the blood runs, the pigs come running".

Palermo, the headquarters of the Sicilian Mafia, has been peaceful for a decade now after the centralised leadership of Cosa Nostra decided to ban killings in order to survive. Naples has always been more chaotic than that, because the Camorra have always been split into clans: 20 are active today. Turf wars erupt perennially amid the grim 1960s estates where they are concentrated. Unemployment is catastrophically high among the city's young people; 58 per cent according to a recent report. Drug dependency is equally high. Those without education and lacking the nous to migrate have few choices. Tens of millions of euros per month are made from the city's drugs trade. That other popular standby, protection money, is also an immensely lucrative racket for the Camorra.

Police believe that the clans will make ¤4bn (£2.8m) from extortion alone. But the latest war, with its nonchalant daylight assassinations, gang-manned roadblocks barring "civilian" traffic into the heartlands of the feuding clans, and the murder of those only vaguely linked to the intended victims, has taken the city's woes to a tragic new level.

Paradoxically, it all began with a police initiative, when they took out a warrant for the arrest of Paolo di Lauro. Nicknamed "Ciruzzo the Millionaire", he was the head of di Lauro clan, and a modern Naples success story. For years he had been the obedient underling of one of the legendary Camorra capi, a gangster called Aniello la Monica. He was present at a famous summit meeting of mafiosi in the early 1980s, when his boss parlayed with Michele Greco, capo di capi of the Sicilian Mafia, "the Pope" as he was nicknamed, "the very archetype of a mafia capo", according to John Dickie in his book Cosa Nostra, "unsmiling, taciturn, given to speaking only in maxims and allusive parables".

Di Lauro was also there among the mourners after la Monica was murdered, when the shopkeepers of Secondigliano, the "quartiere" where he ruled, hauled down their shutters as a sign of respect. Di Lauro's grief was in no way diminished by the fact that, as several supergrasses have since claimed, he was implicated in his boss's murder.

All that of course is so much dirty water under the bridge. Di Lauro had learnt plenty from his dead master and, despite a niggling and semi-permanent feud with a nearby clan called the Licciardi, he kept his donkeys ­ "the Spaniards" as they are widely known because of their endless trips ferrying drugs from Galicia in Spain ­ and his street pushers and the other components of his empire under brutally tight control. And he prospered mightily.

Di Lauro's drug revenue from all his sellers is reckoned by Italian investigators to be worth about ¤200m per year. He funnelled the proceeds into real estate, buying dozens of flats in Naples, owning shops in France and the Netherlands, as well as businesses importing fur, fake fur and lingerie.

Naples is as lackadaisical as it is wild: so little confidence is placed in the police that recently a teenager persuaded her father to murder the thief who stole her scooter. But even in Naples the brilliant career of Ciruzzo the Millionaire could not be ignored indefinitely. Two years ago, the police took out a warrant for Di Lauro's arrest on drug-trafficking charges and, at the age of 51, he went to ground.

He has not shown his face in public since. Last year, he was put on Interpol's wanted list for extradition to Italy in the event of his capture abroad.

Di Lauro had made ample provision for the future, producing 10 children with his wife Luisa, though one has died in a car crash and another is in jail.

But the young man to whom leadership of the clan passed, Cosimo di Lauro, 25, has failed the test. From his old mentor Don Aniello, Cosimo's father had learnt, according to Peter Gomez writing in L'Espresso magazine, "that shooting is not a good idea. Or rather, if you really have to do it, you should to it in silence, without fuss."

But that is a lesson that young Cosimo di Lauro, "very arrogant and with no experience" according to Gomez, has failed to absorb. Two years after his takeover, with his father's steely grip on the clan only a memory, the di Lauro gang split in two. The former boss's lieutenants took advantage of the new leader's weakness to grab a big share of the city's lucrative drug trade for themselves.

The reaction of di Lauro and those who stuck by him was swift and bloody.

The first to die in the current feud were two gang members, Fulvio Montanino and Claudio Salerno, on 28 October. Since then, hardly a day has gone by without one side or the other spilling blood, as each side seeks to up the ante with ever gorier acts of vengeance.

The peak to date came a little over two weeks ago, on the weekend of 22 and 23 November, when six people were murdered in the city in a little over 24 hours. As ever in this current war, the watchword was casual, apparently careless ostentation. On the Sunday morning, for example, a little after 10am, two men sauntered into a tobacconist and calmly shot the owner and one of his relatives, both said to be implicated in the anti-di Lauro rebellion. One of them died at once, the other on the way to hospital.

The so-called "secessionist" gang's reply to that attack came within less than half an hour. A 63-year-old member of the di Lauro gang was reading a newspaper in his car when two rebel gangsters turned up and shot him five times in the face. They dragged the body into their own Ford Fiesta then drove to a nearby suburb of the city and burnt both the car and the victim.

It is fair to say that, up to that point, Naples's new gang war had probably left most of Italy ­ even most people in the city itself ­ pretty cold.

These were punks and thugs bumping off other punks and thugs, after all. It was nothing to get too worked up about. But it was the following day that the cruelty of this latest feud took a ghastly new turn. Gelsomina Verde, recently turned 21, was walking at night along a private road at the edge of Secondigliano, the di Lauro clan's heartland, when she was abducted.

The true target of her kidnappers was a gang member called Vincenzo, a friend of hers, possibly her lover. What happened that night has been reconstructed by the police. Gelsomina was brutally beaten, probably in an effort to get her to disclose her friend's whereabouts. She was then shot at point-blank range in the neck and her body put in a car that was set on fire.

With Gelsomina Verde's death, Italy woke up, and realised the new Naples gang war had got out of hand. The governor of the Campania region (of which Naples is the capital) Antonio Bassolino ­ once compared to New York's Rudolph Giuliani for his success in cleaning up the city ­ said "This challenge must be met and the state must pay attention."

Two days later, Home Minister Giuseppe Pisanu dispatched 325 extra police to a city that already has a higher ratio of police to people than any other in the country. Yesterday, in the first obvious police success, an operation involving 1,500 police netted the modest total of 52 suspected gangsters.

The "pigs" have indeed come running but there is no indication they will succeed in stanching the blood. "We need the old bosses back," one gangster lamented in Corriere della Sera newspaper yesterday. "The war will only end," a Camorra expert predicted, "when one group prevails."