BEIJING, June 22 (Reuters) - A gas explosion at a barbecue restaurant on Wednesday night in China's northwestern Ningxia region killed 31, according to state-run Xinhua news agency, prompting President Xi Jinping to order stronger safety checks.

The blast in Yinchuan, capital of Ningxia region, was caused by a leaking liquefied petroleum gas tank at the restaurant, Xinhua reported on Thursday.

Seven people were still undergoing treatment for burns and cuts from broken glass, Xinhua said.

Xi told authorities to go all out to treat the wounded, and said safety supervision in key industries and sectors should be strengthened, China state television reported.

Accidents due to gas and chemical blasts are not uncommon in China despite years of attempts to improve safety.

In 2015, a series of explosions in the northern port city of Tianjin killed 173 people.