JINAN - Heavy fog in East China's Shandong province has triggered a backlog of flights in the capital city of Jinan, stranding thousands of travelers on Monday.

People ride in heavy fog in Liaocheng city, Shandong province on Feb 25. [Photo/Xinhua]

As of 12:30 pm, four of the 22 flights scheduled to take off on Monday were canceled with the rest delayed, according to Jinan International Airport.

Provincial meteorological authorities have issued an orange fog alert on Monday morning, orange being the second-highest level in China's three-tier color-coded warning system.

Low visibility has also led to the temporary closure of 64 highway toll gates.