Long underwear season has officially started, the Beijing Meteorological Bureau announced Thursday, warning the first winter snow will arrive on Saturday, followed by three more days of sub-zero temperatures.

"The weather will be so cold that you will still feel cold even if you wear your long thermal underpants," the bureau said.

The city's central heating system will also kick in Sunday, 11 days earlier than normal. And flu season has already started, with Beijing health authorities advising residents to get their flu shots.

The government said that it is well prepared to deal with the unusual early snowfall, which is not expected to be very heavy.

There are 5,776 snow clearing devices on standby to clear the streets, and the city has prepared 22,000 tons of snow-melting agent, the Beijing Evening News reported Thursday.

Not everyone is in favor of following the meteorological bureau's advice about wrapping up warmly.

"I don't wear long underwear because without it my legs will look thinner, although my parents believe I should start wearing them now or I will have arthritis when I am older," said 21-year-old Beijing resident  Gao Jialei.

But others are firmly in favor of an extra layer of protection.

"My foreign ex-boyfriend used to make fun of them," said a young professional woman who did not want to be named, who said she has already started wearing them.

Ma Yanming, spokesman for the Beijing Health Bureau, had some advice for stylish young women who wear short skirts or shorts in the winter.

"It's fine if those young girls have cars or just shop all day, because they are in heated places. But if that's not the case, they should wear long underwear," Ma said.

He also noted Chinese people should no longer follow the traditional advice of wearing fewer layers of clothes as the winter starts in order to get acclimatized to the cold, and keep wearing warm layers of clothes even as the spring comes in order not to shock the body by shedding layers too suddenly.

Officials reminded residents that free flu shots are available for seniors and students.

"The flu season will last until next January, and we encourage local residents to get inoculated  as soon as possible," said a media official, surnamed Fu, from Beijing Centers for Diseases Control and Prevention.

Free inoculations are available for seniors over 60 with a hukou (household registration), and for all students, including those from overseas, at primary and middle schools.

Others wanting the injections can get them for between 50 and 89 yuan ($8-14) at 448 clinics in the city, which can be consulted through the healthcare hotline at 12320, he said.

"Over 910,000 people were  vaccinated up to Monday, and we're expecting more," said Fu.