A stone lion on a bridge in Tianjin is covered with a mask in the heavy smog that has hit much of the country's northern regions. [Photo by TONG YU For China Daily]

A combination of pollution and heavy fog affected countless road, rail and air passengers across northern China on Wednesday.

By 4:30 pm, 154 flights had been canceled at Tianjin Binhai International Airport, with another 120 delayed. A total of 450 flights were scheduled to arrive and depart during the day.

The city also closed all 20 freeways due to low visibility in the morning, although half were reopened at 2 pm, according to the local transportation commission.

At Shijiangzhuang Zhengding International Airport in Hebei province, 88 flights were canceled and 17 delayed as of noon on Wednesday.

All trans-provincial bus service from Beijing Capital International Airport was suspended.

Zhou Caixiang bought tickets to fly from Zhengzhou, capital of Henan province, to her home city of Shenzhen in Guangdong province, weeks ago. However, on Wednesday she abandoned the plan due to heavy smog. The 26-year-old instead bought seats on the bullet train.

"It is better to spend hours on a train than waiting anxiously at an airport," she said, adding that the journey takes two hours by air and seven hours by high-speed rail.

At least 32 cities have issued red alerts for air pollution, the highest emergency response in the four-tiered system, the Ministry of Environmental Protection said.

The lingering smog has made Beijing extend its orange alert, which started on Dec 30, until Saturday.