The latest two deaths in China - a 10-year-old girl in the south and a 35-year-old man in the east- followed confirmation by WHO of two bird flu fatalities in Turkey.
The Chinese girl, surnamed Tang, had been sick with a fever and pneumonia since 23 November and underwent emergency treatment, according to the state media. She died on 16 December.
The man, a self-employed vendor, developed the same symptoms on 4 December, the state media said. Identified only by his surname, Guo, he had been recovering in the hospital. He died on 30 December.
Scientists fear H5N1 could mutate into a form that can spread easily between people, leading to a pandemic.
"To put it mildly, it's a serious problem everywhere, not just in China," said Roy Wadia, the WHO's spokesman in Beijing.
The death toll from bird flu in China now stands at five. China's health ministry had previously announced that two women died in eastern Anhui province and another in southeast Fujian province.
Chinese and foreign health officials have said that China's size and lack of resources mean that not every bird or even human case of bird flu is properly identified, making fighting the disease that much harder.
China, meanwhile, has confirmed a fresh outbreak of bird flu among quail on a farm in the poor, southwestern province of Guizhou, the Agriculture Ministry said, bringing the total number of poultry outbreaks to more than 30 since the start of 2005 in China.
Nations across the globe are on
alert over the bird flu scare
The outbreak early this month killed 16,000 quail near Guizhou's capital of Guiyang. They were later confirmed to have the H5N1 strain of the virus, and another 42,000 birds were culled to prevent its spread.
"After the outbreak happened, the Agriculture Ministry immediately sent an expert group to lead the prevention and control work," the ministry report said.
The outbreak has been brought under control, the report added.
Two teenagers died last week from bird flu in eastern Turkey - the first reported deaths from the virus outside China and Southeast Asia. Their dead sister is also a suspected victim and hundreds of Turks have rushed to hospitals for bird flu tests.
Turkey has reported that at least a dozen people are infected with the virus, mostly children. Cases have been confirmed as far west as the central region around the capital Ankara sparking fears the disease could spread to people in mainland Europe.
Aljazeera, meanwhile, has reported the Turksih Prime Minister Rajab Tayib Erdogan as saying that the situation was under control. Massive culling operations are under way and thousands of birds across the country have been eliminated.
Omar Khashram, Aljazeera's correspondent in Turkey, said the authorities have launched a massive campaign to educate people about bird flu and dispel unfounded fears.
Health officials are handing out leaflets, and imams are issuing warnings from mosque loudspeakers in the mostly Muslim country.
Amid such frenetic activity, Shigeru Omi, WHO’s Asian regional director, urged nations to be ready to respond rapidly to any signs of a pandemic.
"To put it mildly, it's a serious problem everywhere, not just in China"
WHO spokesman in Beijing
"Unlike the influenza pandemics of the past, this time the world has been given a warning that one may be on its way," Omi said in a statement. "We should use this precious time to be ready to counterattack and try to stop any sign of a pandemic in its tracks."
Omi is in Tokyo to attend a two-day meeting scheduled to begin on Thursday, focusing on the need for early detection and early reporting, as well as measures that can be taken if a pandemic strikes.
Participants include China, Indonesia, Vietnam, Thailand and South Korea.
European governments, jittery about a potential pandemic, sprayed down trucks from Turkey with disinfectant. In Italy, a consumer group urged the government to impose a ban on travel to Turkey, and in Greece, veterinary inspectors stepped up border checks.