Extreme air pollution in the Chinese capital Beijing has prompted authorities to increase the level of health warnings and order the temporary shut down of more than 100 factories.

Authorities urged the city's 20 million people on Wednesday to stay indoors and shut windows, eat a "balanced diet" and drink plenty of water. A third of all government vehicles have also been ordered off the road.

The director of Beijing's children's hospital said earlier this week that the "continuous smoggy weather has significantly increased the number of child patients".