At least 31 people were killed after a gas explosion at a barbeque restaurant in Yinchuan, capital of northwest China’s Ningxia Hui Autonomous Region, on Wednesday, local media reports said citing authorities.

The blast, as per reports, took place at 9 PM. An investigation into the incident is underway.

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“Thirty-one people were killed after a gas explosion ripped through a barbecue restaurant in Yinchuan, capital of northwest China’s Ningxia Hui Autonomous Region, on Wednesday night, according to local authorities,” CGTN reported.

As per Chinese news agency Xinhua, the blast was caused by a leaking liquefied petroleum gas tank at the restaurant. Seven people were still undergoing treatment for burns and cuts from broken glass.

People were gathering on the street on the eve of the Dragon Boat Festival holiday, the official Xinhua News Agency said. The festival is a national holiday in China. People eat rice dumplings and race boats manned by teams of paddlers.

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The Paper, which is an online publication, cited a woman saying that she was about 50 meters (164 feet) from the restaurant when she heard the explosion. Identified by her surname – Chen – she added that two waiters emerge from the restaurant afterward, one of whom collapsed immediately. Thick smoke came out from the restaurant.

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Meanwhile, the Central Government’s Ministry of Emergency Management said that search and rescue work at the restaurant was completed early Thursday. The cause of the blast has not been revealed yet.

Local fire authorities sent 20 vehicles and more than 100 personnel to the scene, local media reported. President Xi Jinping called the explosion ‘heartbreaking’. He said that it was a ‘profound lesson’.