BEIJING—At least 12 people were killed and 39 seriously injured Sunday after a gas line explosion tore through a residential neighborhood in central China. Responders to the early morning blast in the city of Shiyan in Hubei province sent more than 150 people to the hospital, according to officials quoted by state media. The cause of the explosion remains under investigation. Stall keepers and customers buying breakfast and fresh vegetables at a food market were the majority of victims when the explosion hit shortly after 6 a.m., according to the reports. The blast struck a two-story building built in the early 1990s, which includes pharmacies, restaurants and other businesses. More than 900 people were evacuated from the area. The Shiyan explosion came a day after eight people died and three others were injured when toxic methyl formate leaked from a vehicle at a chemical handling facility in the southwestern city …