The woman, a 41-year old factory worker from the south-eastern province of Fujian, died from the H5N1 form of the virus over a week ago, Xinhua news agency said.
She had apparently contracted the disease in an area that had not officially reported previous outbreaks among birds.
The WHO and other international health bodies have called on China to pass on animal samples of the bird flu virus for testing, which China has not done.
"It means that there is a question mark that hangs over the progress of the virus in China," said Roy Wadia, the WHO's Beijing-based spokesman. "It's perhaps more significant to get animal viruses, because this virus is still something that is primarily in the animal sector."
A Taiwan official complained on Friday his government had not received direct information from Beijing about the death in Fujian, directly across the Taiwan Strait from the self-governed island, and said China was deliberately withholding information.