A gas explosion in a restaurant in northern China has killed at least 31 people, Chinese state news agency Xinhua reported on Thursday.

Seven others were injured, one of them seriously in the explosion on Wednesday night, Xinhua said.

The explosion happened at a barbecue restaurant in the Chinese city of Yinchuan, in the north-western Ningxia region.

The cause which was probably a gas leak led to many deaths.

China’s state and party leader Xi Jinping ordered a full investigation into the incident, which happened on the eve of the Dragon Boat Festival, a public holiday.

Nine people suspected of being responsible were arrested, including the manager, a shareholder of the restaurant and employees, state television reported.

Their bank accounts had  been frozen.

The municipal government said that a restaurant employee and a cook had noticed the smell of gas about an hour before the blast.

They realised that the valve of a gas tank had broken.

Another employee was sent to buy a new valve.

The explosion occurred while it was being replaced, the statement said.

State media reported that a gas tank on the ground floor exploded first, rupturing a gas pipe on the first floor.

The first floor contained rooms with karaoke facilities, where a large number of guests were having dinner, according to the news website Fengmian Xinwen.

It was not initially known why the restaurant was not evacuated immediately after the smell of gas was detected and the defective valve was discovered.

People from neighbouring houses were brought to safety in nearby hotels after the incident.

Rescue workers were trying to establish the identity of the victims.

Twenty fire engine and about 100 emergency personnel and volunteers were mobilised, state media reported. (dpa/NAN)