Health authorities in southern China said Tuesday that a 26-year-old woman has died of a strain of bird flu, and another woman is reportedly in serious condition.

The two contracted H5N6, a strain of bird flu that has so far only been seen in people in China.

A press officer at Shenzhen's Center for Disease Control and Prevention confirmed the death of the local woman on Dec. 30. He wouldn't identify himself.

A 40-year-old woman also from Guangdong province is in serious condition in hospital, the official Xinhua News Agency reported.

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Six human cases of H5N6 have been reported in total, all in China, since May 2014. The virus has been detected in poultry in China, Lao and Vietnam.

The World Health Organization says that human cases of bird flu remain uncommon, with sporadic cases occurring following exposure to infected poultry or a contaminated environment. It says there is no evidence of sustained human-to-human transmission of bird flu.