BEIJING (Reuters) - China has reported a fresh outbreak of bird flu as fears grow across the world of an impending pandemic, a senior U.N. official said on Tuesday. 

The latest outbreak, among geese, was in a village in the suburbs of Tianchang city in the eastern province of Anhui, Noureddin Mona, of the U.N. Food and Agriculture Organisation, told Reuters. 

He said the Ministry of Agriculture had told him on Monday 2,100 birds had been infected, 550 had died and 45,000 had been culled. 

"We are highly concerned about this," he said of the outbreak, adding that the area had been sealed off at a radius of five km. 

The World Health Organization has said the H5N1 strain of bird flu is endemic in poultry in China and across much of Asia, and it may only be a matter of time before it develops the ability to pass easily from human to human. 

China's sheer size and its attempts to conceal the SARS epidemic in 2003 have prompted fears among some experts that it has had more bird flu cases than officially recorded. 

"I think that, now, China is unlike (it was) during SARS," Mona said. "They are highly concerned and have no option but to report." 

The Ministry of Health denied a Hong Kong newspaper report that China would close its borders if a single case of human-to-human transmission of bird flu occurred. 

"The report is inaccurate," a ministry official told the China Daily. 

Since an outbreak in late 2003 in South Korea, the deadly H5N1 strain of influenza has killed more than 60 people in four Asian countries and reached as far west as European Russia, Turkey and Romania, tracking the paths of migratory birds. 

Russia confirmed more bird flu cases on Monday, raising fears it could spread over Europe.