Mount Mau Son in Lang Son Province, 170 kilometers (106 miles) to the northeast of Hanoi, recorded temperatures dropping to minus 2 degrees Celsius (28.4 degrees Fahrenheit) on Friday morning, according to the National Center for Hydro-Meteorological Forecasting.

At the top of Phia Oac Mountain in Cao Bang Province, temperatures also dropped to minus 1 degree Celsius, with ice appearing at an altitude of 1,400 meters and above.

Temperatures in Dong Van Town of Ha Giang plunged to 2 degrees Celsius, and in Sa Pa, a popular tourist town in Lao Cai Province, to 3 degrees Celsius.

At a height of 1,500 meters above sea level, Mau Son was the first to be hit by the strong cold front that arrived in Vietnam's northern mountainous region Thursday, and is expected to last until next Wednesday.

Hoang Lang Huy, a local resident, said thick frost started appearing on Mau Son on Thursday night."The two-kilometer-long road from a salmon farm to the top of Mau Son is covered in icy frost. This was the first time this winter frost has appeared here," Huy noted.

In Meo Vac District of Ha Giang, local residents said frost had also spread across many areas Friday morning.

The Red River Delta recorded temperatures as low as 8 degrees Celsius in Bac Giang and 9 degrees Celsius in Hai Duong Province.

Temperatures in Hanoi's Ba Vi District plunged to 8 degrees Celsius and in the downtown area to 11 degrees Celsius.

Over 800,000 students in Lang Son, Lao Cai, Cao Bang, Hai Duong provinces and the nearby Hai Phong City have been allowed to stay home to avoid the cold grip from Friday.

In other northern provinces, school hours will start later than usual while outdoor activities are limited.

Hanoi authorities have not issued an official decision on whether to allow students to stay home amid the chilly front, though schools have recommended that parents keep their children home should temperatures drop below 10 degrees Celsius.

The center forecast in January-February that northern and central provinces from Thanh Hoa to Thua Thien Hue would experience temperatures of 0.5-1 degrees Celsius lower than the average of prior years.

In response to the cold conditions, weather forecast centers have been urged to increase their daily weather updates, particularly for ethnic minorities in remote, mountainous regions, and those employed outdoors.

Vietnam is expected to experience a colder winter than usual this year as the Pacific Ocean sea surface temperature drops, forming the La Niña phenomenon, weather experts said. The country should expect up to 27 waves of cold air coming from the north this winter, a typical average.