President Michel Martelly laid a wreath Tuesday at the mass grave north of the capital of victims of a catastrophic earthquake that killed a quarter-of-a-million people in the poorest country in the Americas.

Throughout the day Haitians flocked to churches to mark the second anniversary of the 7.0-magnitude quake.

The flattened presidential palace and Port-au-Prince's hollowed-out cathedral offered striking symbols of the failure of an international aid effort that never lived up to its promise, despite billions of pledged dollars.

By the ruins of the Cathedral of Our Lady of the Assumption, whose roof and towers collapsed after the quake, Jean Wilbert, a 40-year-old cripple ekes out an existence in a makeshift camp with his mother.

"I've been here for the past two years," Wilbert told AFP, admitting he found it hard emotionally to move on from the disaster. "I cannot detach myself from this place where I lost my two legs," he said.

UN fact sheets highlighted the hundreds of thousands of people relocated from tent cities in 2011 and the 1.1 million children now receiving daily food aid, but the pace of reconstruction has been painfully slow.

That is partly explained by the cataclysmic scale of the January 12, 2010 disaster, which killed, injured or displaced one in six of the Caribbean nation's entire population, razing some 250,000 homes in the capital alone.

But Haiti was also already the economic basket case of the Western Hemisphere, a dysfunctional country often ruled by a corrupt elite while 80 percent of the population lived below the poverty line, most in stinking slums.

More than half-a-million people displaced by the 2010 quake subsist in 800 squalid tent camps around the capital, and the health authorities, propped up by an army of NGOs, are still battling a cholera epidemic that has killed nearly 7,000 people since November 2010.

In this largely Roman Catholic country, places of worship were holding services throughout the day to remember the disaster, throwing open their doors to quake survivors, many still traumatized by the events of that day.

Government officers were shuttered along with schools and businesses.

At 4:53 pm local time (2153 GMT), the moment the earthquake struck, President Michel Martelly laid the wreath at the mass grave north of the capital where most of the dead lie entombed, dumped there in lorry-load after lorry-load in the days after the disaster.

Martelly vowed to press on with reconstruction: "For two years, we have mourned our dead, healed our wounds -- we must now rebuild."

UN chief Ban Ki-moon paid tribute to those who died -- including more than 100 UN personnel -- and called on international donors to keep up their "vital support" for the rebuilding two years after the disaster.

"Despite considerable achievements, including in the areas of rubble removal and the resettlement of displaced persons, many Haitians remain in need of international assistance," Ban said.

UN special envoy to Haiti Michaelle Jean said "murderous negligence" had contributed to the vast toll as she pointed to "an absence of laws and regulations to standardize construction works" that led to building collapses.

"It is irresponsible laissez-faire, generalized disorder set up as a system," she said.

Shocked in the immediate aftermath of one of the deadliest disasters of modern times, the international community promised billions of dollars of aid money to "build back better."

Decentralization -- away from the slum-infested, sprawling capital of three million -- was the buzzword in a plan to be implemented under the watchful eye of former US president Bill Clinton.

This grandiose vision now appears to have been a pipe-dream.

Less than half the $4.59 billion pledged has been received and disbursed, and the coffers of the aid agencies are also drying up.

More than 50 percent of the quake rubble has now been cleared, but little has been erected in its place.

Most of the hundreds of thousands of people who fled Port-au-Prince after the quake have since returned to the overcrowded capital, desperate for work and food in a country still lacking another effective pole to attract labor.

Martelly, a former carnival entertainer and pop singer, was sworn in as the new president in May, riding a populist wave and promising to bring the change that the country so badly needs.

But faced with a parliament dominated by his political opponents, it took him five months to even get a prime minister appointed.