KUNMING, Dec. 3 (Xinhua) -- Five people are being questioned by police following a lethal coal mine gas blast in southwest China's Yunnan Province on Sunday morning that killed nine miners.

The five are Zhang Hua, manager of the mine, Gan Jiahuan, deputy manager, and three other safety workers, according to a statement released by the Zhenxiong county government.

They have been ordered to cooperate with police inquiries and prevented from leaving the county.

An explosion occurred at 8:30 a.m. on Sunday in the Shizishan coal mine in Zhenxiong when 52 miners were working underground.

Thirty-six, whose working sites were unaffected by the blast, were evacuated unharmed. In another working site containing 16 miners, eight were killed at the scene and one died in hospital. Seven were injured, two of whom are in a critical condition.

All coal mines in the county were ordered to suspend operations on Monday to prepare for safety inspections.

The privately owned Shizishan mine had an approved production capacity of 90,000 tons a year.

The cause of the blast is still being investigated.