Venezuelan President Hugo Chavez (left) embraces his daughter Rosines during a ceremony to register his candidacy for the presidency at the National Elections Council in Caracas.

Caracas - Venezuelan President Hugo Chavez led his biggest rally since he was diagnosed with cancer a year ago, seeking to stage a show of strength on Monday as he heads into a re-election campaign to extend his 13 years of socialist rule.

Chavez stood on top of a truck as it drove through huge crowds of supporters who cheered and threw roses and confetti as he made a dramatic re-entry into the public eye after months of keeping a low profile during cancer treatment.

The rally in Caracas was all the more important after his opposition rival, Henrique Capriles, put on a show of youthful vigour on Sunday by leading a 10km march with hundreds of thousands of supporters to register his candidacy.

“I give this to you with a promise to fight, to battle, and of course to win,” the 57-year-old Chavez said as he handed electoral officials his plan for government.

He had entered the building appearing to walk with some difficulty, hand-in-hand with two of his daughters.

That prompted a scathing response from Capriles on Twitter: “This candidate isn't walking, he is out of gasoline! A better future of progress is coming!”

Outside, several giant inflatable Chavez dolls waved their arms above the crowd as the president's fans danced to music pounding from speakers. Hundreds of buses that ferried his followers to Caracas stood parked in side streets.

“Look at this sea of people, look at the happiness,” said Esther Martinez, a 66-year-old retiree dancing in a city square. “For every person that came out yesterday, we've brought out 10, 20, 30 more. And that's going to be reflected in the election.”

Any turn for the worse in Chavez's health could mean the end for his movement. That would be a blow to global leftist leaders who see him as an inspiration, but a boon to investors seeking free market reforms in Venezuela and oil companies keen on tapping the world's biggest crude reserves.

His allies have kept his image in the public eye for months with rallies from which he was notably absent or appeared only via Twitter messages that cabinet ministers read out live.

Chavez has at times seemed to revel in the rumours of his imminent demise, which range from him being confined to a wheelchair to reports that he has only two months to live.

Last year he said he underwent two operations to remove a baseball-sized tumour, and this year had a third operation only months after having declared himself “cancer free”. His true condition is a guarded state secret.

“Chavez is the best thing this country and the world have ever had. He is kind and humane,” said Aracelis Aguilera, a 55-year-old secretary.

Most of the country's main pollsters show Chavez holding a double-digit lead over Capriles. But Venezuela's public opinion is known to shift dramatically, as it did when Chavez came from behind in 1998 to win his first election.

On Saturday, Chavez spoke extensively with reporters, joking and telling stories while standing on the steps of the presidential palace in a live television appearance.

He said a battery of medical exams had come out “absolutely fine”, but did not say whether he would need more treatment.

Supporters sent Twitter messages with the hash tag #VoyconChavez (#I'mgoingwithChavez). Adversaries responded by filling Venezuela's notoriously vitriolic Twitter-sphere with messages tagged to #13anosdementiras (#13yearsoflies).

Critics accuse Chavez allies of using state resources to swell demonstrations and forcing government employees to attend.

Opposition leader Leopoldo Lopez said the ruling Socialist Party had ordered ministries to help bring 120 000 people to the march, citing what he called an internal party document. - Reuters