An explosion near a chemical plant in China's northern Hebei province early on Wednesday killed 22 people and injured at least 22 others.

A video of the blast scene in Zhangjiakou city shared by state media showed billowing black smoke and flames, while photographs showed rows of burned-out cars and trucks lining the streets.

The fire engulfed 50 vehicles, the official Xinhua news agency reported, citing governmentsources.

State media said all fires at the blast site had been extinguished.

An official news release said the blast occurred just after midnight at a loading dock next to the plant operated by the Hebei Shenghua Chemical Industry Co Ltd.

Zhangjiakou, a city about 156km northwest of Beijing, is set to host the 2022 Winter Olympics alongside the capital Beijing.

The explosion occurred at the entrance of the factory when a vehicle transporting dangerous chemicals blew up, according to The Paper, a news outlet that cited a staffer at the Zhangjiakou City Safety Production Supervision Administration.

"On-site search and rescue work and investigation of the cause of the accident are still under way," the Propaganda Department said.

Three decades of swift economic growth in China have been marred by incidents ranging from deadly mining disasters to factory fires, but public anger over safety standards has grown.

China has vowed to improve industrial standards but environmentalists say they fear oversight weaknesses persist, including an opaque production process for hazardous chemicals.

In August 2015, 165 people were killed after a chemical warehouse explosion in the port city of Tianjin. A government report found the disaster was caused by hazardous materials that had been improperly or illegally stored. (Aljazeera)

• The scene after an explosion at a chemical plant in Zhangjiakou City in China's Hebei province [Courtesy: Xinhua news agency]