CHENGDU -- Four people have been confirmed dead after a roof collapsed in a coal mine in Southwest China's Sichuan province last Saturday, local authorities said Thursday.

The accident occurred at around 11 am last Saturday in the Changshi'er coal mine in the city of Wanyuan, initially leaving four miners unaccounted for.

After days of search and rescue efforts, all four missing miners were found by 11:30 pm Wednesday, but none showed signs of life, rescue officials told Xinhua.

Rescue teams from various levels responded swiftly, but efforts were hindered by high gas concentrations, weak structural supports, damaged tunnel roofs and floors, and large, unstable coal gangue prone to sliding within the mine shaft. To prevent secondary disasters, rescuers had to carry out search operations in a more scientific and cautious manner.

The coal mine owner has been detained by police and an investigation is underway.