At least four people were killed Tuesday in an explosion that occurred in a restaurant in China, media reported.The explosion shattered the restaurant in east China's Fujian province, Xinhua reported citing an official."Three more people remain in a critical condition," the official added.Police are investigating the explosion and an initial investigation showed it to be caused by a gas cylinder. Fire officers continue to clear the site.Locals said the restaurant, which was on the ground floor of a residential building, was a popular eatery, but lacked safety equipment such as fire extinguishers.