PORT-AU-PRINCE (AFP) - Haiti went to the polls Sunday to choose if a popular singer or a former first lady will be the new president of a shattered country struggling to rebuild from a devastating 2010 earthquake. The run-off, delayed for months by bickering over a contested and violence-plagued first round in November, threatened to be overshadowed by the return from exile of charismatic ex-president Jean-Bertrand Aristide. But Aristide has largely honored a commitment not to upset the delicate political situation and voting began peacefully in the Caribbean nation, whose recent past has been scarred by dictatorship and violent upheaval. Six hours after voting stations opened at 6:00 am (1000 GMT), UN monitors said turnout looked likely to exceed pitiful numbers in the first round when only 23 percent of 4.7 million eligible Haitians cast ballots. "I've seen a lot of differences compared to November 28. Participation is greater," said Edmond Mulet, head of the UN peacekeeping mission MINUSTAH. Polls were scheduled to close at 4:00 pm (2100 GMT) with preliminary results to be announced on March 31 and final ones on April 16. The international community is watching closely as it has committed billions of dollars to help reconstruct Haiti, where hundreds of thousands of quake survivors are forced to eke out an existence in squalid tent cities. The election is a study in contrasts, pitting Mirlande Manigat, a 70-year-old academic and former first lady, against Michel Martelly, a 50-year-old singer and carnival performer known to his fans as "Sweet Micky." They are vying for the job of rebuilding a nation beset by problems, from endemic poverty and corruption to the quake-shattered infrastructure and a cholera epidemic that has claimed almost 5,000 lives since mid-October. Pre-election opinion polls showed Martelly, a political novice with a colorful past, enjoying a slim lead over the more softly-spoken Manigat, but experts warned that such forecasts are notoriously unreliable in Haiti. Early voting appeared free of major problems, although observers reported "irregularities" at some polling stations, including poll workers arriving late at Croix-des-Bouquets, a large voting center outside the capital. Colin Granderson, a former Jamaican prime minister who as number two of the regional bloc CARICOM is leading an international observer mission in Haiti, said it was too early to tell how widespread the irregularities were. The problems, however, appeared minor compared to November when polling stations were trashed and the whole process deteriorated into a farce when most of the candidates called for a re-run even before the polls had closed. At least five people were killed in December when days of rioting erupted at the news that Martelly had finished third behind ruling party candidate Jude Celestin and would not make the run-off. After weeks of US-led pressure and a review by international monitors, Martelly was eventually reinstated at the expense of Celestin, who was seen as current President Rene Preval's handpicked successor. On the eve of Sunday's vote, UN chief Ban Ki-moon said Haitians had a "historic opportunity to shape the future of their country," which is recovering from the Jan 2010 quake that killed more than 220,000 people. Watching from the sidelines are two former presidents and foes - Aristide and Jean-Claude "Baby Doc" Duvalier, who made a shock return to Haiti in January, ending his own 25-year exile. Aristide, 57, wasted no time in wading into the fray on his return from South Africa on Friday, seven years after being driven from power by a rebellion 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. But Aristide, who rose as a champion of the poor to become Haiti's first democratically elected president, stopped short of backing a particular candidate, which could have potentially altered the outcome of the race. Ousted from office twice, once in a 1991 military coup and then again in 2004, Aristide burst onto the political scene in 1985 to oppose Duvalier's authoritarian rule and challenge the entrenched elite. Their presence again in Haiti represents an unsettling political wildcard for whoever emerges as Sunday's victor and looms over a process that will be key to any chance the desperately poor nation has of a recovery.