Two more people have died from H7N9 bird flu, bringing the death toll to 20.

Six more cases make the number of case climb to 102. Five of the new cases were in Zhejiang province and one was in Shanghai. Of those, 70 patients are still in hospital and 12 have been discharged. 

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"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," the WHO said In a statement.

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

China announced the first case of human infection of the H7N9 in late March.