Eight coal miners were killed and 13 trapped inside the Jiangjiawan mine near the city of Datong in northern China, when a shaft flooded, state news reports said Tuesday. About 247 workers were reportedly inside the mine when the accident occurred on Monday.

The rescue efforts are ongoing and over 600 rescue workers are pumping water and drilling in an effort to reach those who are still trapped. On Monday, workers retrieved the bodies of those who were killed in the accident. Four of the 17 miners, who were trapped inside the mine, were rescued on Tuesday and taken to a nearby hospital, Xinhua reported. One of the rescued miners, however, died.

Four pumps were reportedly extracting water from the shaft; about 3,840 cubic meters of water was removed by Tuesday morning. The coal mine is owned by Datong Coal Mine Group and can produce 900,000 tons annually, Xinhua reported. Following the incident, the company suspended production at all its small coal mines to conduct safety checks after a preliminary investigation into the accident showed that the flooding happened because water was accumulated in an underground area at the colliery.

Last year, the number of deaths due to coal mine accidents dropped to 931, according to the State Administration of Work Safety, cited by Xinhua. A report by the Associated Press said that the fall in the number of accidents at coal mines was mainly due to increased safety and lower demand for coal.