Dressed in their best and clutching Bibles, thousands of Haitians have gathered in a ruined cathedral to mark the moment a year ago when the earth convulsed and savaged their nation.
"It's a day of reflection and of prayer," said Roger Jean, 64, who lost his wife and three children that day, 12 months ago, when a 7.0 earthquake shattered the impoverished Caribbean nation.
More than 220,000 people were killed almost instantly, and 1.3 left homeless when at 4:53 pm (2153 GMT) on January 12, 2010 the earth heaved for a few terrifying seconds, collapsing homes and businesses, churches and schools - leaving hellish scenes of devastation and suffering.
"I am addressing a special prayer for Haiti to God: a prayer for Haiti to change, that Haiti live again," Jean said.
About 2,000 people on Wednesday spilled out of one of the thousands of tent cities, which still dot the capital Port-au-Prince, lying just behind the shattered cathedral.
Later on Wednesday the nation was to observe a minute of silence at the exact moment that disaster struck.
The anniversary finds Haiti barely healed from the trauma and gripped by political uncertainty over the holding of a runoff round in elections to replace President Rene Preval.
The economy and infrastructure remain crippled, a cholera outbreak continues to kill, and more than 800,000 people live in squalid tent camps, according to a new official count. Rebuilding has hardly begun.
Former US president Bill Clinton, one of the main figures coordinating a massive international aid effort, arrived on Tuesday to join ceremonies and said he was "frustrated" by the slow pace of reconstruction.
He also called on the government "to resolve" an election stand-off.
However, he did say he was "encouraged" that after repeated delays in organising the flow of aid money and the implementation of promised projects, "we are doing much better."
Huge challenges remain, including clearing rubble, moving people out of tents, halting widespread environmental degradation, and rebuilding an education system with less than half of all children currently in school.
International donors have pledged almost $US10 billion ($A10.15 billion) to reconstruct Haiti, but a year after the earthquake little of it has reached the country.
One immediate concern is the cholera outbreak, which has so far claimed 3,759 lives, according to the latest Haitian government update, and sickened thousands more.
One of the toughest issues to resolve is the stalemate in holding a second round in the presidential election to replace Preval.
International monitors from the Organisation of American States (OAS) are due to issue a report with non-binding recommendations to Preval on how to move ahead after first-round results sparked deadly riots.
According to a leaked draft of the report, the OAS is calling on Preval's favoured successor Jude Celestin to drop out because of fraud.
Celestin would step aside in favour of the previously third placed candidate, singer Michel Martelly, who would then face Mirlande Manigat, a former first lady who won the most votes in the first round.
The switch, if confirmed, would be a blow to Preval, who is due to leave power and had been hoping to see his ally take over.
Some observers fear Haitians could face a renewal of rioting that claimed five lives after last month's announcement of preliminary results.
