Residents walk on a snowy road in Urumqi, capital of Northwest China's Xinjiang Uygur autonomous region, Dec 11, 2015. A snowstorm hit Urumqi on Dec 11 and the local meteorological bureau has issued a red alert for snowfall. [Photo/Xinhua]

URUMQI - Heavy snow has disrupted air traffic and forced schools to close in northwestern China's Xinjiang Uygur autonomous region, local authorities said on Friday.

As of noon on Friday, about four dozen flights to or from Urumqi Diwopu International Airport had been canceled, rerouted or delayed, sources with the airport said.

Runways at the airport were closed twice to clear ice and snow from the ground.

Urumqi education bureau issued an emergency notice on Friday afternoon, ordering all the junior middle and primary schools to suspend classes immediately.

A cold front descended on the region on Thursday, causing snow in most of the region. In Urumqi, the regional capital, snow piled up to a record 37 centimeters on Friday.

About 10,000 cleaners and 1,500 snow removal machines are working in the city to deal with the snow.

The snow has decreased since Friday noon and is expected to end early on Saturday morning. Flights at other airports in Xinjiang have not been affected.