An unexpectedly early snow fell on Beijing and other cities in North China on Friday, causing traffic dilemmas for millions of people, and prompting the capital to start providing heating for residential complexes ahead of schedule.

According to the National Meteorological Center, the snowfall hit areas in Beijing, Hebei, Shanxi and Shandong provinces, and the Inner Mongolia autonomous region. The snow will continue until Sunday in most of the region.

The snowfall is the earliest in Beijing since a blizzard hit the capital on Nov 2, 2009. Meteorological experts said the snow will be helpful for growing wheat in North China and warned that residents should be careful to avoid carbon monoxide poisoning as the heating starts to work.

"People should keep an eye out and ventilate their homes to get rid of carbon monoxide emitted by heating equipment, especially for those who have seniors at home," said Zhang Fanghua, chief weather forecaster of the National Meteorological Center.

Beijing routinely provides heating beginning on Nov 15, but it can be shifted to an early date if the temperature is lower than 5 C for five consecutive days. Weather forecasts show that the snow will not stop in the coming four days. Beijing Environment Sanitation Engineering Group announced that the heating system for residential complexes would start eight days ahead of schedule to make sure that every household in the capital has access to heating.

Beijing traffic police said traffic accidents during Friday morning rush hour increased by 30 percent due to the weather. About 50 flights had been canceled at the Beijing Capital International Airport as of press time.

According to the World Meteorological Organization, the periodic El Nino event may be one of the strongest in more than half a century and cause irregularities in the global climate. Early snowfall is also part of its consequences, and meteorological experts have warned people around the world to be prepared for its side effects.

However, Zhang pointed out the benefits from snow.

"The snowfall will be good for agriculture as the snow can provide water to the dry land in Henan and Shandong provinces, and the low temperatures can kill pests and pathogens that lurk in the land," she said.

huyongqi@chinadaily.com.cn