BEIJING - A man in the north-eastern Chinese province of Shandong has been infected by a new strain of bird flu, the first case found in the province, state news agency Xinhua reported.

The death toll from the H7N9 virus that recently emerged in humans has also risen to 22, after an 86-year-old man in eastern Zhejiang died on Tuesday.

It is still not clear how people are becoming infected and the World Health Organisation (WHO) says there is no evidence of the most worrying scenario - sustained transmission between people.

The latest patient, a 36-year-old man from the city of Zaozhuang in Shandong. is being treated in hospital. A total of nine people in close contact with the victim are under observation but have shown no signs of infection, Xinhua said.

Another two people have also been infected in eastern Zhejiang province, the agency said.

So far, 109 people have contracted the disease since the first deaths were reported in China last month.

Investigators have yet to determine human-to-human transmission of the virus.

"Investigations into the possible sources of infection and reservoirs of the virus are ongoing," WHO said on Monday.

"Until the source of infection has been identified, it is expected that there will be further cases of human infection with the virus in China," said WHO.

The WHO's China representative, Mr Michael O'Leary, issued data last Friday showing that half of the patients analysed had no known contact with poultry, the most obvious potential source, but he said it appeared that human-to-human transmission was rare.