Police officials said they were testing the poisonous gas that killed the workers and had detained an unspecified number of people in connection with the incident.
A gas leak has killed at least 18 people working in a coal mine in central China's Hunan province, state media reported on Monday.
Another 37 miners were rescued and taken to a hospital for treatment following Sunday's accident at the Jilinqiao mine in Huangfengqiao township, according to Xinhua news agency, citing local authorities.
Investigators are testing the gas while police have detained an unspecified number of people in connection with the accident, Xinhua said.
China is the world's largest coal producer, and deadly accidents in mines are common.
Seventeen coal miners were killed when a lift used to move workers fell down a shaft in northeastern Heilongjiang province in March.
In December, explosions in two separate coal mines in the Inner Mongolia region and in Heilongjiang killed at least 59 people.
Thirty-three miners were killed in a colliery explosion in October in the southwestern municipality of Chongqing, and in September at least 18 were killed in a mine blast in the northwestern Ningxia region.