All poultry bought at established markets, and properly cooked, is safe to eat, Yu Kangzhen, chief veterinarian at the Ministry of Agriculture, said on Monday.

"The source and transmission of H7N9 bird flu remain unclear, but the virus should be destroyed by high temperatures," he said.

The ministry said 20 variants of the H7N9 strain were detected from 738 samples taken at three live poultry markets in Shanghai on Thursday and Friday.