BEIJING - A powerful 7.8-magnitude quake struck Monday close to densely populated areas of southwestern China, killing at least five people and rattling cities across a swathe of southeast Asia.

At least four children were killed and more than 100 injured when the quake toppled two primary schools in the vast city of Chongqing near the epicentre, China's official Xinhua news agency reported.

Another person was killed in neighbouring Sichuan province by a collapsing water tower, Xinhua added, saying President Hu Jintao had urged an "all-out" effort to rescue victims.

More people were feared dead after a local official said "rows of houses" had collapsed in Dujiangyan, a city with a population of 600,000.

Military troops were ordered to help with the disaster relief work and the international airport at Chengdu, nearer the epicentre, was closed.

Xinhua said Premier Wen Jiabao was on his way to the region.

The quake struck 93 kilometres from Chengdu, capital of Sichuan province and a city of more than 12 million people, and about 260 kilometres from Chongqing and its 30 million.

The State Seismological Bureau located its epicentre in Wenchuan County, a mountainous region home to the Wolong Nature Reserve, China's leading research and breeding base for endangered giant pandas.

Xinhua quoted an official saying the landmark Three Gorges Dam in Sichuan province had not been affected.

However, buildings shook in Beijing and Shanghai, residents reported, with many people evacuating tower blocks and rushing onto the street. There were no immediate reports of damage there.

"There was a lot of shaking. I felt a bit dizzy," said Lilian Wu, who is a marketing official with a fund management firm on the 37th floor of Shanghai's landmark Jinmao Tower.

Tremors were also felt in Bangkok, Hong Kong, Hanoi and Taipei, residents there said.

Both the Chinese seismological bureau and the US Geological Survey, which use different scales, measured it at 7.8.

The quake struck shortly before 2.30 pm (0630 GMT), according to the USGS, at a depth of just 10 kilometres.

A reporter for CCTV news in Chengdu said residents had poured out onto the streets but public transport and electricity supplies remained operational.

However, the tremor appeared to have disrupted cellular telecommunications in the city, he added.

State television also said there appeared to be no infrastructure problems in Chongqing.

The phone network in Chengdu and elsewhere around the country appeared to suffer a meltdown as people tried to find out what happened.

Two residents near downtown Chengdu whom AFP contacted by phone said they felt a violent shaking that threw glassware to the floor and toppled street lights.

However, they were not sure whether the quake had caused significant damage in the city as they had not yet ventured far from their home.

Further information could not be obtained as the connection was cut.

The quake was felt in the Taiwanese capital Taipei, where buildings swayed for half a minute, and in the southern Chinese territory of Hong Kong.

In Hanoi, residents said some high buildings shook for around five minutes but there were no reports of damage.

The last powerful quake to hit China was on March 21, a 7.2 magnitude quake which struck near the northwestern city of Hotan in Xinjiang province.

A reporter for Hong Kong-based Cable News based in Kunming, the capital of southwestern Yunnan province which borders Sichuan, said he saw many people running onto the streets to find out what had happened.

"One office worker working on the 11th floor of a building in Kunming told me that the lamps in his office were shaking and he felt dizzy," the reporter told the local broadcaster.

One of the biggest quakes ever recorded was in China in 1976, which killed 242,000 people.

That quake, centred in the northern city of Tangshan, lasted for 15 seconds and flattened 90 percent of buildings. The death toll, out of a population of one million, made it one of the world's deadliest in the 20th century.

In 1920 and again in 1927, separate quakes in northwestern China each left some 200,000 dead. - AFP/ir