An aftershock has brought new havoc to the earthquake-stricken region of China on Friday.

The aftershock, measuring 5.9 on the Richter scale, hit Lixian, to the west of the epicentre in Wenchuan, Sichuan, cutting newly repaired roads and telecommunications.

China put the known death toll at just over 22,000 on Friday but has said it expects it to eventually exceed 50,000. About 4.8 million people have lost their homes.

The country is also on precautionary alert against possible radiation leaks, according to a government Web site.

The disaster area is home to China's chief nuclear weapons research lab in Mianyang, as well as several secretive atomic sites, but no nuclear power stations.

Thousands of residents from Beichuan, one of the places worst hit, streamed away from the town carrying babies, bags and suitcases.

And thousands of men, women and children were heading on foot for Mianyang, a city near the epicentre, saying they were abandoning their ruined villages for good.

Anger has focused on the state of school buildings, many of which crumpled in Monday's 7.9 magnitude quake, burying thousands of children and prompting the Housing Ministry to order an investigation.

In Dujiangyan, a school collapse buried 900 students. In Wufu, nearly every building in the village withstood the quake but for a primary school, whose collapse killed about 300.

China has sent 130,000 troops to the disaster area, but with buckled and blocked roads, supplies and rescuers have struggled to reach the worst-hit areas.

The first foreign rescue teams, from Japan, Russia, Taiwan, South Korea and Singapore have also arrived in Sichuan province.

At China's request, the World Food Programme said it was sending enough ready-to-eat meals for 118,000 people.

UN Secretary-General Ban Ki-moon announced emergency funds of up to seven million dollars and said more would be available.

The United States said it had provided China with satellite images of earthquake-stricken areas, and would send two planeloads of relief for victims this weekend.

Hundreds of damaged dams have also raised fears of collapse and flooding of areas struggling to recover from the quake.

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