URUMQI - Heavy fog left over 8,000 passengers stranded on Wednesday in the airport of Urumqi, capital of Northwest China's Xinjiang Uygur autonomous region, airport authorities said.

More than 40 outbound flights were delayed, and another 17 Urumqi-bound flights were diverted to other airports as fog blanketed the airport Wednesday morning, reducing visibility to about 200 meters as of 3:00 pm, said a spokesman with the Operation Control Center of the Xinjiang Airport Group.

The fog had continued to linger by press time.

Heavy fog was also to blame for a 13-vehicle pile-up on an expressway linking Turpan with Urumqi on Wednesday morning. Four people were killed, and nine others injured in the accident, according to local rescuers.