BEIJING - One year after a massive earthquake devastated parts of Sichuan Province, China paused Tuesday to remember the nearly 90,000 people left dead or missing by the disaster and to thank international donors for their help with the recovery effort.

Women grieve in the earthquake-devastated town of Beichuan in China's Sichuan province on May 10. Chinese President Hu Jintao has led the nation in a minute's silence at the epicentre of the powerful Sichuan earthquake that flattened homes and communities one year ago. (AFP/File/Peter Parks) But the anniversary was dogged by continuing questions about the deaths of thousands of Sichuan children crushed in the rubble of school buildings that the Chinese government says were solidly built, but many parents insist were substandard.

President Hu Jintao led a ceremony Tuesday at the quake's epicenter, in the leveled town of Beichuan, shortly before 2:30 p.m., the time the quake occurred on May 12, 2008. Mr. Hu adjusted the flowers on a single, large memorial wreath adorned with a red sash.

Parents of dead students gathered at the wreckage of Beichuan Middle School, where about 1,300 of the 2,900 students and teachers perished. They lighted incense and candles and heaped floral tributes to the dead.

The middle school's collapse during the 7.9-magnitude earthquake, even as nearby buildings withstood the shock, unleashed a flood of bitter accusations from parents and friends of the dead students that cheap materials and corner-cutting building methods had made the school building vulnerable to a quake. Parents in other towns where schools had similarly collapsed joined the outcry, and engineers and building experts who examined the schools' rubble supported them.

Seeking to calm the turmoil, the government issued a report last week stating that official inquiries had found no evidence that poor construction contributed to the school collapses. The report said for the first time that 5,335 students had died in the earthquake.

Some survivors have rejected the report's conclusion, and charged that the official death toll is too low.

On Monday, Mr. Hu thanked foreign diplomats who were invited to the quake commemoration ceremony for their nations' contributions to relief efforts, saying they had demonstrated "grand humanitarianism and friendship with the Chinese people."

The government said that 160 nations and assorted international organizations had donated more than $11 billion to quake relief efforts, and that their rescue teams had given medical care to 10,000 survivors and saved one victim who had been buried in the wreckage.