PORT-AU-PRINCE – Haitians went to the polls on Sunday to choose between a popular singer and a former first lady as the quake-ravaged country's next leader in an environment dominated by the return of ex-president Jean-Bertrand Aristide.

Voting began throughout the country at 6:00 am (1000 GMT), as scheduled, an AFP correspondent reported.

Mirlande Manigat, a 70-year-old academic and ex-first lady, and singer Michel Martelly, 50, are competing for the job of rebuilding a nation beset by deep poverty, a quake-shattered infrastructure and a cholera epidemic.

The vote ends a long and turbulent election season that sparked fraud charges and deadly violence after a first round of balloting in November in the race to succeed President Rene Preval.

The latest survey, out Thursday, showed Martelly ahead with 53 percent support against 47 percent for Manigat.

However, experts warn that historically weak voter turnout makes forecasts unreliable: just 23 percent of 4.7 million eligible voters cast ballots in the first round November 28.

Manigat won the most votes in a corruption-plagued first round, but "Sweet Micky" Martelly, a bawdy carnival singer who laces performances with fierce political satire, has high name recognition and strong support among the country's young.

On the eve of the vote, UN Secretary General Ban Ki-moon reminded Haitians it was a "historic opportunity to shape the future of their country," which is recovering from the January 2010 earthquake that killed 220,000 people.

Ban expressed hope that Haitians will go to the polls "in a calm and peaceful atmosphere."

Watching from the sidelines are two former presidents and foes -- Aristide and Jean-Claude "Baby Doc" Duvalier -- whose recent returns from exile are reminders of Haiti's history of violent political upheaval.

Aristide, 57, lost no time wading into the political fray on his return Friday, seven years after being driven from power by a rebellion and under US and French pressure.

"Haiti's ills have worsened," the former shantytown priest said in a televised speech moments after stepping off a private jet from South Africa with his family.

The return of Aristide -- a champion of the poor whose own regime was criticized for engaging in political intimidation and human rights abuses -- just two days before the election is a political wildcard for whoever emerges as the victor in Sunday's balloting. Results of the second round are due to be released April 16.

Thousands of cheering supporters welcomed home Aristide, who blasted authorities for barring his Fanmi Lavalas party from the Sunday vote.

"The exclusion of Fanmi Lavalas is an exclusion of the majority of Haitians," he said.

Vernon Jean, a Haitian political analyst, said the date of Aristide's return was no coincidence.

"One has the impression that the people are looking for a leader that they have not found since Aristide's departure. He is going to position himself as the indispensable leader," Jean told AFP.

A Western diplomat posted here told AFP on condition of anonymity that Aristide's return "could be an additional element of trouble. There is a need for a serene social and political climate. His return can only add to the confusion."

But Dan Beeton, an analyst at the Center for Economic and Policy Research, said Aristide's euphoric reception "underscores the contrast between a leader who many Haitians think looked out for them and the two presidential candidates who do not enjoy the same support."

Aristide burst onto the political scene in 1985 to oppose Duvalier's authoritarian rule. "Baby Doc" fled the country amid an uprising in 1986, but made a shock return in January from his own 25-year exile.

Haitian prosecutors have charged Duvalier, now 59, with corruption, embezzlement of public funds and criminal association during his 15-year rule.

Haiti's 4.7 million eligible voters will also vote for members of the country's legislature.

Some 800,000 Haitians still live in tent cities more than a year after the earthquake that devastated the capital city, killing 220,000 and leaving more than a million people homeless.

Poll were scheduled to close at 4:00 pm (2100 GMT). Preliminary results were to be announced on March 31 and the final ones on April 16.