Heavy fog continued to shroud the northern parts of China Tuesday, causing fatal road accidents, closure of highways and delay or cancel of flights.

The affected areas include the provinces of Heilongjiang, Jilin, Liaoning and Shaanxi, Ningxia Hui Autonomous Region, Tianjin, Shandong and Beijing.

Two people died after a bus and a truck collided Tuesday on an expressway in Yongning County of Ningxia Hui Autonomous Region. Initial investigation showed that the poor visibility should be blamed, said the county traffic police.

Ningxia's weathermen said the visibility in Yinchuan was less than 50 meters and that on some parts of the expressway linking Ningxia and northwestern Qinghai Province, drivers couldn't see five meters away.

Northeastern Liaoning Province issued the 20th fog alert since Nov. 3, saying fog was shrouding most parts of central Liaoning and the visibility in Shenyang and Dalian cities was less than 200 meters.

All of the fifteen expressways leading into Liaoning were closed. More than 100 flights to and from Shenyang airport were delayed and so were most of the flights at Dalian airport.

In Harbin City, capital of northeastern Heilongjiang Province, four expressways were partially closed and 20 flights were delayed as fog reduced visibility to less than 50 meters.

Four expressways in northwestern Shaanxi Province were partially closed due to the fog that had reduced visibility to less than 200 meters.

Three expressways with visibility of less than 20 meters in northeastern Jilin Province were closed.

The visibility in most part of Tianjin was less than 50 meters, according to the weather station. All the expressways in Tianjin were closed and flights were delayed.

As of 9 p.m., 32 flights were canceled in Jinan, capital of east China's Shandong Province. The beltway of the city was closed as of 9:30 p.m. as the visibility had been reduced to less than 100 meters.

As of 11 p.m., the visibility in Beijing was reduced to 100 to 500 meters, and highways from Beijing to Tianjin, Shenyang and other nearby cities had to be shut down.

The fog was expected to become thicker on Wednesday in the capital city, said Guo Hu, director of the Beijing Meteorological Station.