Following weeks of near-seclusion, Chavez announced by letter that he was travelling to Havana for hyperbaric oxygenation therapy, a treatment designed to reduce radiation therapy-induced bone decay.

Hyperbaric oxygenation therapy, or HBOT, involves breathing pure oxygen in a pressurized chamber.

In addition to the bone-weakening side effects of radiation on cancer patients, experts say HBOT is used to treat conditions including infections and abscesses, as well as decompression sickness, or “the bends", sometimes experienced by deep sea divers.

The Venezuelan public, who have speculated about the 58-year-old’s cancer since it was diagnosed last year, are uncertain about the implications of this latest development and are wondering whether it is standard post-radiation treatment or a serious setback.

Chavez appeared exhausted at the end of his presidential re-election bid in October and later admitted that the radiation had taken its toll.

The usually high profile leader has made brief and infrequent public appearances, mainly on state TV, since his October 7 victory, prompting one opposition newspaper to dub him "The Invisible Man".

In contrast with previous trips to Cuba for treatment on two tumours in his pelvic area, state TV did not air coverage of the president departing Venezuela or arriving in Cuba, moreover.

While it is unclear when Chavez will return, he aims to be back for the January 10 start of his new term, and possibly earlier for a couple of regional summits.

The president’s absence leaves newly appointed Vice President Nicolas Maduro in a prominent position amid speculation among Venezuelans over who could replace Chavez should he leave power.

Congress head Diosdado Cabello is also considered to be a possible successor to lead the ruling Socialist Party. Under the constitution, an election would have to be held if Chavez were to leave office within the first four years of his new six-year term.

Opposition leader Henrique Capriles, who ran against Chavez in the presidential poll, sent him best wishes for a "long life" but also urged greater transparency.

"Nobody wants to play the rumour game," he told reporters. "Venezuelans should be told with total transparency what the situation is, what's the extent of this treatment. That's the way it should be in Venezuela and how it is in other countries."