BEIJING, Dec 13 (Reuters) - Chinese authorities warned from Tuesday most of the country faced heavy snowfall, blizzards and plunging temperatures this week in what could be one of the coldest December snaps in China in decades.

Beijing is expected to be hit by temperatures as low as minus 18 degrees Celsius (minus 0.4 degrees Fahrenheit) this weekend compared to around minus 8 C on average in mid-December. Even Shanghai in the south could be buffeted by weather as frigid as minus 4 C on Saturday through Sunday, unusual for this time of the year.

Having issued its second highest alert for blizzards, Beijing shut all schools from Wednesday and moved learning online, while firms were encouraged to offer employees flexibility for work and staggered commutes.

In a safety caution message, the capital warned of avoiding snow hazard areas and asked residents to reduce travel and closely monitor as well as remove snow from the top of long-span buildings and facilities.

Heavy snow is expected to hit Beijing's Capital Airport between Wednesday morning and early Friday.

Parts of north, northwest and south China, as well as parts of the Inner Mongolia region, Guizhou province and even regions south of the Yangtze River, could see temperatures slide by more than 14 degrees C, the National Meteorological Center (NMC) cautioned.

It has called on local governments to take precautions against the cold weather, advised the public to keep warm, and urged measures to be taken to protect tropical crops and aquatic produce.

Until Friday, the NMC forecast large-scale rain and snowfall in central and eastern regions of the country, bringing as much as 30 mm (1.2 inches) of precipitation in snowstorms in parts of Shaanxi, Henan and Shandong.

Many rivers in Heilongjiang, a vast northeastern province that shares a border with Russia, have already frozen over.

Also on Tuesday, the China Meteorological Administration activated a Level-II emergency response - its second-highest emergency response level - for the cold wave and blizzards.

In Beijing, more than 6,000 people have been put on call for any road emergency rescues and 2,200 sets of snow-removal equipment and machinery are on standby for deployment.

Additionally, 32,000 tonnes of snow-thawing agent is ready for use on icy roads and motorways.

The city authorities also encouraged voluntary participation in snow clearing and ice shoveling operations even as 73,000 people have been placed on duty, and required indoor heating be ramped up in all districts.

The Chinese capital last saw such cold weather on Jan. 7, 2021, when the temperature fell to minus 19.6 C.

The cold snap in Beijing this week, compared with the autumn-like conditions a week ago, reflects the sharp oscillations in temperatures recently. In October, Beijing experienced one of its warmest Octobers in decades in a year of weather extremes.

Beijing's all-time low temperature was minus 27.4 C, set on Feb. 22, 1966.

Photo from Reuters