Four people have been put in police custody after being found responsible for a coal mine fire that killed nine people and injured one in northwest China's Shaanxi Province a month ago, local authorities said Saturday.

The accident occurred at about 7 p.m. on April 1 in Quanzigou Coal Mine in Longmen Township, Hancheng City. Initial investigation showed the accident was caused by dereliction of duty, the municipal government said in a statement.

Police have detained mine manager Zhu Shouhuai, a deputy manager, a mine captain and a gas inspector.

The mine has a designed annual production capacity of 60,000 tonnes.