BEIJING - CHINA said on Friday it had not yet identified why a large number of schools collapsed in the Sichuan earthquake, killing thousands of students and devastating bereaved parents.

'Up to now we haven't found that anybody caused or did anything to make the building vulnerable so that it collapsed and people died when the earthquake struck,' said Tang Kai, a planning official, just days ahead of the quake anniversary. 'The job is huge and the workload is very heavy,' Mr Tang, a senior official at the ministry of housing and urban-rural development, told reporters.

The collapse of schools when the 8.0-magnitude quake hit the southwestern province of Sichuan on May 12 last year is one of the most sensitive aspects of the disaster, as critics say this was due to shoddily-constructed buildings.

According to a first official tally made public on Thursday, 5,335 students died or went missing in the earthquake - lower than initial estimates - as their classrooms collapsed while nearby structures stood firm.

Bereaved parents have demanded a report into why so many school buildings fell apart so easily, but Mr Tang said identifying the cause was a difficult process. Investigators still had to figure out if there were problems with the design, construction process, supervision or maintenance, he said.

His comments came as China promised to step up the pace of reconstruction in Sichuan and neighbouring affected provinces Gansu and Shaanxi, saying it would complete the process a year ahead of schedule.

Mu Hong, another top planning official, said that under initial plans from September last year, 'we decided it would take three years for all the recovery and reconstruction efforts to be completed'.

'Now we have decided that we will accelerate the process so that it will be completed in two years, which means the finishing line is September 2010.' Mu is vice chairman of the National Development and Reform Commission which has planning control over the economy.

The massive May 12 quake left nearly 87,000 people dead or missing and more than five million others homeless, and a large part of the reconstruction has been aimed at rebuilding homes, schools and hospitals.

Mr Mu said that by the end of April 2009, around 360 billion yuan (S$77 billion) had been invested in more than 21,000 projects in Sichuan, Gansu and Shaanxi. -- AFP