QINGDAO-- Low visibility caused by heavy fog forced the closure of the Qingdao Liuting Airport in East China's Shandong province Tuesday morning.

Nearly 2,000 passengers were stranded after 20 flights were canceled, an airport official said, adding that heavy fog has blanketed parts of the city of Qingdao since early morning, with visibility reduced to less than 100 meters in some areas.

The airport has initiated a contingency plan for the foggy weather.

The Qingdao meteorological department has issued an orange fog alert, the second level in China's four-tier color-coded weather warning system.

Some highways were also forced to close because of the fog, according to the Shandong Expressway Group.