BEIJING -- The H7N9 bird flu has killed 45 people on the Chinese mainland since the first human infection was confirmed in late March, a health official said on Thursday.

A total of 135 cases of H7N9 infections have been confirmed, with 134 on the mainland and one in Taiwan, said Wang Yu, director with the Chinese Center for Disease Control and Prevention.

Wang was speaking at an international symposium on the prevention and treatment of new types of influenza.

"There are still many unknown conditions relating to the H7N9 bird flu virus as well as diseases that might result from it, and the risks of pandemic influenza caused by a new type of avian influenza virus should not be underestimated," Wang said.