BEIJING, Dec 4 (Reuters) - A Siberian cold front swept China on Thursday, with temperatures in the capital plunging below freezing and thousands stranded on snowbound expressways in the remote far northwest.

The state weather observatory launched a cold weather emergency response plan on Wednesday to tackle disasters after record cold and snow brought down power lines and paralysed much of the usually mild south earlier this year.

And hundreds of thousands of people made homeless by the devastating May 12 earthquake are sleeping in tents or temporary housing in the mountains of Sichuan and surrounding southwestern provinces where temperatures at night can fall well below freezing.

In the restive northwestern region of Xinjiang, home to minority Uighurs, about 3,400 people were stranded on blocked expressways after two days of snow, the China Daily said.

Temperatures in the region have plunged by about 18 degrees Celsius as snowstorms also hit northern Inner Mongolia and Gansu province. In Beijing, temperatures plunged about 10 degrees overnight to minus 3 Celsius (27 degrees Fahrenheit).

China issued an extreme cold weather warning on Wednesday, ordering 23 provinces to be on standby for emergencies.

In Sichuan, an official said last month that many quake victims were still short of basics, including quilts and even food, for the winter.

But a local propaganda official in Beichuan county, one of the hardest hit, told Reuters on Thursday the government had made efforts to ensure everyone would survive the winter safely.

The worst snowstorms in 50 years hit southern China in January and February, leaving millions of Lunar New Year travellers stranded on their way home for the holiday. (Reporting by Beijing newsroom; Editing by Nick Macfie)

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