The new suspected cases, in addition to three confirmed outbreaks in southwest and central provinces of China, came after the World Health Organisation (WHO) warned the outbreak there could be far larger than reported.
Of the latest suspected outbreaks in China, two were detected in eastern Anhui province, one in the eastern coastal metropolis of Shanghai, and the other in the southern province of Guangdong, the Xinhua news agency said.
The WHO said that given China's size and its vast poultry industry, there was only a "small window of opportunity" to prevent a major outbreak of the disease.
"It's entirely possible that there are outbreaks elsewhere (in China) that have not been reported," Beijing-based WHO spokesman Roy Wadia said.
"If there are small, isolated outbreaks, it could be entirely possible it could be unnoticed. This could cause the virus to spread faster," he said, urging Beijing to improve co-operation and prevention measures swiftly.
After Beijing announced the four new suspected outbreaks, Hong Kong said it had suspended the import of all live birds and poultry meat from the whole of mainland China.
It had already banned imports from Guangxi, Hunan and Hubei provinces.
"It's entirely possible that there are outbreaks elsewhere (in China) that have not been reported. If there are small, isolated outbreaks, it could be entirely possible it could be unnoticed. This could cause the virus to spread faster"
World Health Organisation
Meanwhile, the WHO said on Friday 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 centres received two weeks ago a sample from a country that we are not naming that had been taken last April," she said.
The outbreaks, which have killed 10 people in Vietnam and Thailand and infected millions of poultry in 10 Asian countries, were first reported in South Korea on 15 December last year.
Health experts have warned that while humans have so far only caught the disease through contact with infected birds or their droppings, it could claim millions of lives if the H5N1 strain mutated into a more contagious form.
Only about 200,000 chickens and ducks have been culled in China, but more than 25 million poultry have been slaughtered across the rest of the region as Asia's main weapon against the outbreaks.
But the WHO has said there is an increased risk of mutation if the cull in China is not executed properly.
"If (the killing of birds) is done in such a way that exposes more people, then this... could be increasing the risk of developing a strain that you would not want to see," spokesman Dick Thompson said on Thursday.
"From what we can see... many of these culling workers are not wearing the right personal protection equipment. We are also unsure how many of these people have been vaccinated against (normal) influenza."
A British laboratory is working on
a vaccine for the bird flu virus
The UN Food and Agriculture Organisation (FAO) also voiced concern that the mass cullings were not happening fast enough in poorer Asian countries.
"We are... concerned that mass cullings are not taking place at a speed we consider absolutely necessary to contain the virus H5N1 in the region," said Hans Wagner, a scientist with the Rome-based FAO.
World experts on bird flu will meet in Rome next week to plot a strategy for controlling the disease, a FAO source said on Friday.
Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand and Vietnam have all reported outbreaks of H5N1 among poultry, while Taiwan and Pakistan have reported weaker strains of the virus.
Indonesia has come in for heavy criticism over its reluctance to carry out a mass cull to combat the virus which has infected millions of birds there.
President Megawati Sukarnoputri on Thursday ordered the immediate killing of all poultry infected with bird flu following pressure from the WHO.
But Indonesia appeared to backtrack on Friday, with officials saying they would only carry out a selective cull.
WHO Western Pacific spokesman Peter Cordingley said Indonesia should comply with UN Food and Agriculture Organisation recommendations by placing a "sanitary zone or a quarantine area" around infected areas.
This would require killing chickens in farms close to those with confirmed infections.
"We have to cut down on the contact level between chickens and humans," Cordingley said. "It's the only way."
"We have to cut down on the contact level between chickens and humans. It's the only way"
World Health Organisation
In Vietnam, the government said more than half of its 64 provinces and cities had now been hit by the outbreak, as authorities in Hanoi ordered the slaughter of all of the capital's one million chickens.
In Thailand alone 10.7 million chickens have been slaughtered, mostly packed into sacks and buried alive in deep pits in a hasty operation that has been criticised as inhumane and avoidable.
Bird flu vaccine
And in another development, a British laboratory is working to use genetic technology to create a vaccine which could combat the spread of bird flu.
A sample of the live virus was flown in a bomb-proof container from Vietnam to a research laboratory at a biological institute north of London, the BBC said.
"The virus we are using has killed chickens in south Asia, and it has killed humans," virologist Dianne Major told the broadcaster.
Researchers at the National Institute for Biological Standards and Control hope to build a vaccine by combining human and bird - known as avian - flu genes.
This involves first taking a cell from the bird flu virus and then altering its genes to make it safe, before genetic material is then taken from a human flu virus.
The resulting man-made combined virus - which researchers hope could be ready within as little as two months - should then provide the basis of a vaccine.