'I am very saddened by the deaths of students. If investigations show that is the case, it must be dealt with seriously,' he said in Beijing.

'At this stage we cannot rule out the possibility there has been shoddy work and inferior materials.'

Amid fading hopes of rescuing the tens of thousands still buried or missing, anguish is giving way to fury over charges of corruption and dubious construction practices. The disproportionate damage to school buildings and the number of student casualties have also raised public concerns over the quality of educational facilities in many rural areas.

Bloggers and state media have also raised questions after pictures circulated of collapsed schools surrounded by relatively unscathed buildings. Many contributors to online forums have said they believed corruption and shoddy construction were to blame for such a heavy toll.

'These buildings were like tofu,' bristled a netizen on a Net forum. Another cited the fact that many government offices were intact after the devastating quake.

Parents of child victims have started pointing fingers at local officials who are suspected of pocketing money budgeted for construction and at private real estate companies believed to have cut corners.

But Mr Jiang dismissed the widespread belief that school buildings had been disproportionately damaged by the quakes.

He said that school buildings in Sichuan were no more vulnerable to earthquakes than other structures, saying he had found that many other buildings had collapsed near two collapsed school buildings he visited this week. He said that the sheer scale of the quake had gone far beyond the designed resistance of the buildings.

With the death toll over 20,000 and climbing, the industry is facing intense scrutiny for not enforcing earthquake-resistant standards.

Experts said that while there were adequate building codes in place, what was implemented was a different matter - especially in rural areas where regulations were rarely enforced. 'The cutting of corners in a construction industry rife with corruption made matters worse,' said a construction engineer who declined to be named.

Mr Jiang said more than 4 million houses in Sichuan had been destroyed or damaged by the earthquake, according to preliminary estimates, which excluded two of the worst-hit counties. More than 400,000 houses were destroyed or damaged in neighbouring Gansu province and more than 300,000 in Shaanxi , he added.

Tap-water systems in about 20 cities and counties in Sichuan had also been seriously damaged. Power grids and natural gas utilities were also seriously damaged in badly hit regions.

Mr Jiang said the ministry had been mobilising to transport water purifiers, gas cookers and mobile toilets to the quake-stricken regions.