"By Saturday night, the total number of bodies recovered from the airshaft was 55, so that concludes our work," Albertico Guinto Sierra, a spokesman for the local government, told reporters.

It was one of the biggest mass graves ever unearthed in Mexico, he said.

Bordering the Pacific Ocean, Guerrero is one of the Mexican states most affected by violence among drug trafficking gangs that, according to the government, has left over 22,700 dead throughout Mexico in the last three years.

Officials said only four bodies have been positively identified so far, including a state prison warden, strengthening suspicions the airshaft was used by drug gangs to dump the bodies of their victims.

Investigators said the bodies were likely thrown down the airshaft one to six months ago, and that it would take three or four weeks to identify most of the victims.

More than 50 families from around the country have turned up in Guerrero in the past week to find out if their missing relatives are among the bodies found in the airshaft, said Guinto.

He said police were searching for more bodies in 10 wells around the mine, after locals reported a strong stench in the surroundings.

Forty bodies have been deposited at the city morgue in Guerrero capital Chilpancingo, filling it to capacity, officials said. The rest of the human remains were taken to facilities in nearby cities.

Drug-related violence continued unabated in Mexico with six headless bodies found Sunday night, "in a half-hour period," in different parts of Gomez Palacio city, northern Durango state authorities reported Monday.

Two human heads of men 19-33 years of age were found the same night, the state's attorney general's office said in a statement. The four remaining heads were found on Monday.

None of the human remains have been identified so far, the statement added.