Hong Kong ( CNN ) -- Two more people infected with a rare strain of bird flu in China died over the weekend , as the number of human cases of H7N9 climbed to 60 , state media reported Sunday . The two deaths , both in Shanghai , takes the death toll to 13 , the Xinhua news agency said . Shanghai 's health authorities have now reported 24 cases , after three men were diagnosed with H7N9 on Saturday . The virus also appears to have spread beyond eastern China for the first time . Two new cases were reported in central Henan Province on Sunday morning , while a child in Beijing in the north tested positive on Saturday . The H7N9 strain is normally found in birds and was never known to infect people until last month . The World Health Organization ( WHO ) said China had been infected with a new variation of bird flu . The agency said it continued to look for the source of the infection . `` Investigations into the possible sources of infection and reservoirs of the virus are ongoing , '' the organization announced on Saturday . `` 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 . '' So far , WHO said , there is no evidence of ongoing human-to-human transmission . A possible source for the infections is poultry markets , which have become the focus of investigation by China 's health ministry and WHO . Several cities in eastern China have suspended trading in live poultry in an effort to contain the problem . Chinese scientists said the H7N9 virus probably came from migratory birds from East Asia that mixed with domestic fowl around Shanghai . The new variation of bird flu has genetic characteristics that make it well-adapted to infect humans , the New England Journal of Medicine said . CNN 's Hilary Whiteman contributed to this report .
NEW : 13 dead from a total of 60 cases of bird flu in China , authorities say . Comment: H7N9 was never known to infect people until last month . Cases of the virus have now spread to central and northern China .