The number of dead and missing rose to more than 74,000, with a further 247,000 hurt.

But aftershocks, heavy snow on mountain passes, rain and the threat of disease have complicated relief efforts.

Thousands of children died when their schools crumbled around them, prompting widespread claims that corruption fatally compromised the buildings' strength.

Hundreds of distraught relatives placed wreaths along the road leading to Fuxing primary school in Wufu, where at least 127 children were crushed to death. They hoisted a banner reading, "The children did not die of a natural disaster but of an unsafe building."

"An answer must be given to our children," said Li Xiaoping, whose 11-year-old son was among the dead. "There is a problem with the buildings ... all the buildings here did not collapse except for this one building."

Li Rongrong, who heads the state-owned Assets Supervision and Administration Commission and is in charge of overseeing China's huge state sector, told a Beijing news conference that generally construction companies under him were very good.

But he added: "If these buildings (which collapsed) were built by major state-owned firms, we will take severe measures."

In Yinhua town, where more than 200 pupils died, a woman who lost her 13-year-old daughter said the school building had had two levels in 1993, but illegally added two more later.

"When it collapsed it was just fragments, not blocks. That shows how badly built it was," Luo Zaihong said.

A petition circulated in Juyuan town, where 500 or more pupils died in the ruined middle school, demanding punishment of those responsible for shoddy schools, and compensation.

Protests by parents could be troublesome as the ruling Communist Party seeks to maintain a staunch front of unity and stability in the wake of the quake.

FROM RESCUE TO RELIEF

Thousands of aftershocks, heavy snow in the Wenchuan mountains and a forecast of more rain compounded difficulties for military, government and private workers trying to deliver aid and provide shelter.

Some 5 million people were left homeless by the 7.9-magnitude quake. In the countryside, where countless homes are too damaged or unsafe to live in, many farmers now live in encampments of makeshift shelters.

"The biggest hardship we have is not having a tent," said Wang Falan, living with her extended family of 11 in two makeshift shelters. "It is also the lack of rice and cooking oil. I don't know what we'll do if we have to keep living like this."

The Foreign Ministry urged the international community to donate more tents. Three million were needed.

In Washington, Pentagon spokesman Bryan Whitman said a US C-17 transport plane was due to arrive in China with aid supplies on Wednesday. He also said the Bush administration has given Beijing high-altitude spy satellite images of the quake-stricken Sichuan region.

"They specifically asked for images of dams, reservoirs, roads and bridges," Whitman said.

"They made the request so that Chinese experts could better assess the development of the earthquake, its aftermath (and) present conditions, particularly with regard to landslides that could be developing in the area."

Premier Wen Jiabao has warned of the threat of "secondary disasters," ordering experts to inspect dams and reservoirs on 24-hour patrols.

Wen also ordered the supply of 250,000 temporary housing units -- simple steel structures normally used by construction workers -- in the quake area by June 30 and the number should reach 1 million in three months, state media said.

Beichuan, a town totally destroyed by the quake, was closed off due to the threat of disease, a newspaper reported. More than 5,000 epidemic prevention workers had been sent to 125 villages in Sichuan, state media said.