Haiti marked four years since a violent earthquake shattered the impoverished nation, which is still struggling to recover from the widespread devastation that killed 250,000 people.
Haitians, many dressed in white, flocked to church services for sombre remembrances for those who perished in the tragedy on January 12, 2010, which left about a million people homeless.
But four years on, nearly 200,000 people are still living in dire conditions in temporary shelters, and residents complain of getting little help since NGOs left.
President Michel Martelly, who has faced protests over the slow pace of rebuilding, declared the anniversary a "day of reflection and commemoration".
He laid flowers early on Sunday at the site of a mass grave for many of the quake's victims. And he attended a ceremony at 4.53pm, the moment the earthquake struck four years ago.
"Thirty-five seconds ... That's all the time that was needed, on January 12, 2010, to spread darkness over Haiti. We were all in tears, plunged into despair that day," Martelly said.
Wearing white as he addressed thousands of Haitians gathered for a minute of silence in memory of the catastrophe's victims, Martelly also thanked "the friends of Haiti who came from all over to help".
He called for Haiti's 10 million people to unite for reconstruction, saying the Caribbean nation would "move forward with our resources in rebuilding".
"Haiti is like the reed; it bends but does not break," he said.
Flags were to be lowered throughout the country and businesses closed on Sunday to mark the anniversary.
The devastation is still keenly felt in Port-au-Prince, the teeming capital of the Americas' poorest country.
Faced with criticism over the slow pace of rebuilding, especially of administrative buildings - including the legislative palace - Prime Minister Laurent Lamothe had pledged last week to step on "the accelerator to advance the main projects".
But church ministers railed against the time it was taking to reconstruct buildings that were largely levelled throughout the capital.
Opposition critics have attacked the government for failing to make better progress.
"We find ourselves again this January 12, 2014 with sentiments of strong concern ... over our true engagement in the politics of reconstructing the country," senate president Dieuseul Desras said in a statement questioning the government's "ability to respond to social needs".
The government says a large portion of millions donated by governments and organisations the world over was spent on the post-earthquake emergency and not for reconstruction.
"We were lucky to have help from Venezuela. Most of our projects were accomplished with Venezuelan money. With slim means, we accomplished a lot of things," Lamothe said.
He also criticised the international community for failing to provide promised aid of nearly US$9 billion.