(CNN) -- A gas explosion killed 31 people and injured seven on Wednesday night in the northwestern Chinese city of Yinchuan, according to state broadcaster CCTV.
Of the seven injured, one person remains in critical condition. The other six are being treated at the hospital for minor injuries, burns and glass cuts.
The explosion was caused by a leak in a liquefied gas tank inside a barbecue restaurant, according to state media CCTV.
Nine people have been detained by police in connection with the gas explosion in the city of Yinchuan, and their assets were frozen, Chinese state broadcaster CCTV reported.
Police arrested the head of the barbecue restaurant where the explosion occurred, as well as employees and shareholders.
According to a statement from the Yinchuan municipal government, citing interviews with two restaurant employees, an hour before the explosion they smelled a gas leak and discovered that the valve of the liquefied gas tank was broken. They sent another employee who takes care of the kitchen to buy a new valve, and the explosion occurred when the valve was being replaced.
Chinese President Xi Jinping called the incident "heartbreaking" and a "profound lesson," according to a CCTV report.