Two more people in China have died from a new strain of avian influenza, bringing to 16 the number of deaths from the H7N9 virus, and the government has warned that the number of infections could rise.

The latest victims were from the commercial capital of Shanghai, where the majority of the 77 cases have been found, Reuters reported citing the official Xinhua news agency.

The exact source of infection remains unknown and no human-to-human spread of the virus has been confirmed. Samples have tested positive in some birds in poultry markets that remain the focus of investigations by China and the U.N.'s Food and Agriculture Organization (FAO).

Zeng Guang, the chief scientist in charge of epidemiology at the China Disease Prevention and Control Centre (CDPCC), said about 40 percent of the victims have no clear history of poultry exposure, the Beijing News newspaper reported on Wednesday, April 17.

According to a Reuters analysis of the infections, based on state media reports, only 10 out of the 77 victims as of Tuesday have had contact with poultry.

The panic over bird flu has caused many Chinese to shun eating chicken for fear of catching the virus.

China said on Sunday the virus had spread outside the Yangtze River delta region in eastern China, with cases reported in the capital Beijing and the central province of Henan.