The Indonesian president led an emotional ceremony that began with a minute's silence to mark the moment one year ago when the giant waves obliterated the coast of Aceh province in just a few moments.

Some 168,000 Indonesians lost their lives to the tsunami, one of the world's deadliest natural disasters, which was triggered by a massive undersea earthquake off the Indonesian coast.

"We bow our heads in deep prayer so that the souls of the loved ones, found or unfound, at land or at sea, have a proper resting place at God's side," President Susilo Bambang Yudhoyono told a sombre gathering.

"We are here to also honour those who survived. These sons and daughters, brothers and sisters, parents, they all want to regain their lives," he said.

Former US president Bill Clinton, the UN special envoy for tsunami recovery, delivered a pre-recorded message praising reconstruction efforts in Indonesia but warning that "so much more needs to be done".

"Tens of thousands of you are still living in inadequate shelters with poor access to information about the future," he said.

"Let it be known that I won't be satisfied until you have decent homes and job opportunities so that your children can grow up with a renewed sense of security."

UN Secretary General Kofi Annan also warned that more tough times may lie ahead for the region.

"Breadwinners desperately need to regain secure livelihoods, hundreds of thousands of families need to reestablish themselves in permanent homes, and communities need to rebuild," he said in a pre-recorded message.

Some Acehnese, such as Zarkasih, who lost his wife and three young children, marked the day quietly at home.

"If I recall the day when the tsunami struck, my heart is so painful," said the survivor, who was picking coconuts when the waves engulfed his family and swept them away.

"I prayed that they will be given an appropriate place in the hereafter. I know that I will eventually meet them."

At Banda Aceh's Baiturrahman Grand Mosque, where bodies were piled in the days after the tsunami as rescue workers struggled to comprehend the magnitude of the disaster, hundreds of white-clad Acehnese held a morning mass prayer.

In the evening, about a thousand people thronged again to the mosque to pray with President Yudhoyono in the final commemorative event for the day here.

The president urged the Acehnese to keep the peace that the tsunami inspired by pushing both separatist rebels and the government to negotiate an historic pact, ending a nearly three decades-old conflict.

"With our unity there will be an opportunity for us to develop an Aceh which is prosperous, secure and just," he told the crowd. "In the future it is not impossible that Aceh will be more advanced than other regions."

Housewife Maria Ulfa said she was pleased the president was with them.

"I think he's concerned about the welfare of the Acehnese. But it was a shame we didn't get a chance to talk to him," she said.

Mourners converged on mosques across the staunchly Muslim province throughout the day. At one mosque, 43-year-old Hamridar wept as she clutched a photograph of her four dead children.

"I came here to remember my children. I really want to hold them, I have even dreamed of holding them," she said.

In the West Sumatran town of Padang, officials tested the country's newly-installed tsunami early warning system for the first time, with some 2,000 residents fleeing to higher ground as sirens blared.

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