Five people died in a coal mine on Monday evening in Hegang, Heilongjiang province, according to a statement released on Tuesday by Hegang Mining Holding Group Co.
At about 8:30 pm on Monday, a leak occurred as workers injected liquid carbon dioxide in an enclosed area at the group's Xing'an Coal Mine, a preliminary investigation found. Nine people were trapped.
Four of the nine trapped people were rescued.
Investigation into the cause is underway.