The World Health Oganization urged China to swiftly contain the spread of deadly bird flu after authorities confirmed two more areas were affected and announced four new suspected outbreaks, making a total of seven hot spots.

"We have repeatedly said there is a brief window of opportunity to act within China," said Dr Julie Hall, a Beijing-based WHO infectious disease expert.

"This latest news strongly suggests that the window is getting smaller with each passing day," she said in a statement.

As fears of a major outbreak of bird flu in China grew, the authorities widened a chicken export ban to include the three new regions with reported outbreaks including its most populous city, the eastern metropolis of Shanghai.

Hong Kong responded by announcing it had suspended the import of all live birds and poultry meat from the whole of mainland China.

The WHO, which has warned China's outbreak could be far larger than reported, also said Friday that the current wave of bird flu outbreaks sweeping Asia may have appeared as early as April 2003.

WHO spokeswoman Maria Cheng said a similar strain was found in samples that were rechecked by a WHO-affiliated laboratory recently.

"One of our collaborating centers received two weeks ago a sample from a country that we are not naming that had been taken last April," she told AFP, adding that the virus looked to be a similar strain as H5N1.

Asia's first recent bird flu outbreak was reported in South Korea on December 15.

More than 25 million birds have now been culled across Asia to curb the disease which has killed 10 people in Vietnam and Thailand and been detected in chickens in eight other countries.

Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand and Vietnam have all reported outbreaks of H5N1 -- the deadliest strain of the virus -- among poultry, while Taiwan and Pakistan have reported weaker strains.

In Vietnam, where dozens of people remain hospitalised with suspected bird flu, Prime Minister Phan Van Khai imposed a ban on all transport of chicken across the country to fight the virus which has hit two thirds of its 64 provinces.

State media said Khai had asked several ministries including defence and police to set up control stations and prevent the transport of poultry from one locality to another.

The United Nations' Food and Agriculture Organization (FAO) has warned that the mass cullings it considers absolutely necessary to contain the bird flu virus are not happening fast enough in poorer Asian countries.

Hans Wagner, the FAO's senior animal production and health officer, said the Rome-based organization was "concerned that mass cullings are not taking place at a speed we consider absolutely necessary to contain the virus H5N1 in the region."

The warning came as Indonesia appeared to backtrack Friday on a planned mass cull of chickens, with officials saying they would only carry out a selective slaughter despite pressure to join other affected nations in culling flocks.

World experts on bird flu, including specialists from the WHO and the World Organisation for Animal Health will meet in Rome next week to plot a strategy for controlling the disease.

"The aim is to develop a coordinated plan to address animal and public health concerns in each affected country," an FAO source said.