Cold air is forecast to sweep across China and cause a slump in temperatures along with strong wind, as measures have been taken nationwide to ensure people a warm winter.

The National Meteorological Center said that starting from Nov 4, temperatures were forecast to plummet, and wind is expected to blow from the northwestern to southeastern parts of China.

Temperatures are forecast to drop by between 8 C and 10 C, and in some northern areas by 16 C.

"The cold air will bring a plunge in temperatures nationwide compared with mid-October. The cold wave came from west Siberia, which was then enhanced by cold air from the Arctic," said Xue Jianjun, deputy director of the center.

"Heavy snow or rain will take over the Northeast and North China and the Inner Mongolia autonomous region, and farmers there should protect corn outdoors ahead of the precipitation," he said.

Jia Xiaolong, deputy director of the National Climate Center, said it is unlikely that freezing weather will last long or spread widely, though temperatures are forecast to be lower than normal years in central and eastern parts.

In October, La Nina, the periodic cooling of ocean surface temperatures in the central and east-central equatorial Pacific, started to affect China, the National Climate Center said.

"In most winters, when La Nina events reach their peak, cold air tends to hit China more frequently and heavily," Jia said.

In the winter of 2008, which was affected by the La Nina event, China was hit by low-temperature rain, snow and freezing weather, causing deaths, damaging facilities and crops, and affecting 20 provinces and regions, the climate center said.

"The cold rain and snow in South China in 2008 were caused by complicated climatic factors. The cold air was frequent, and conditions for water vapor were good, which made the freezing weather last.

"According to the forecast, water vapor in the southern areas was not as strong as in 2008, so chances are small that large-scale and continuous low-temperature rain and snow will occur," Jia said.

However, he warned people in the eastern part of Southwest China and the western part of the Yangtze River's south that there may be periodic cold rain and snow this winter.

People should also be prepared for weather affecting electricity and traffic, he said.

The central government has taken measures to ensure a warm winter. Power plants nationwide stored 110 million metric tons of coal by Nov 2. Coal supply far exceeded consumption by up to 2.3 million tons to meet heating demand, the National Development and Reform Commission said.

In late September and early October, the provinces of Heilongjiang and Shanxi began to supply heating three to 14 days earlier than normal years, local governments said. Heilongjiang province has improved its heating standard as its minimum indoor temperature increased from 18 C to 20 C, the local government said.