Media playback is unsupported on your device Media caption The WHO says there is currently no evidence of human-to-human transmission of the virus

China has begun a mass slaughter of poultry at a market in Shanghai, after a new bird flu virus was detected there.

The H7N9 virus, a form of avian flu not before seen in humans, was discovered in pigeons being sold in the market.

Six people have now died from the virus, Chinese officials say.

It is not yet known how people are catching the disease, although the WHO says there is currently no evidence of human-to-human transmission.

The virus was discovered in pigeon samples in Huhuai market in western Shanghai, Chinese media said.

There have been 14 confirmed infections so far in eastern China, including in Shanghai and Zhejiang province.

The Chinese government has stepped up its disease surveillance, and has advised people to maintain good personal hygiene, including frequent hand-washing and avoiding direct contact with sick or dead animals.

Meanwhile, the Centers for Disease Control and Prevention in the United States says that it is developing a vaccine in case it is needed.

The virus does not appear to make birds sick, which makes it harder to track down the sources of the virus.

Chinese authorities have covered up health crises in the past, the BBC's Jo Floto from Beijing reports.

This time, however, they say they are doing their best to be as open as possible, our correspondent adds.