The state Xinhua news agency said the shortfall was caused by insufficient coal supplies and a seasonal drought, which limits the production of hydro-electricity.

Shopping centres and department stores will have to turn off their heating for two hours each morning - 1000 until 1200, local time.

Shanghai has already shut down some small factories.

Last week the city of Changsha said it would cut off electricity to most of its residents on one day out of every four.

Correspondents say the shortages illustrate the precarious nature of China's power supply, which has not developed at the same speed as its economy.