One of the four surviving miners is lifted out after being trapped in a collapsed mine 36 days in Pingyi, East China's Shandong province, on Jan 29, 2016. [Photo/Xinhua]

Authorities have intensified an investigation into a collapse at a gypsum mine in Shandong province after four miners trapped more than 200 meters underground for 36 days were rescued on Friday.

They are also preparing to repair land damaged by gypsum mining.

A team comprising experts and government officials was set up on Saturday to investigate the cause of the accident and to help with the search for those still missing, the local government said.

The four survivors rescued on Friday were trapped when the collapse occurred at a mine belonging to the Yurong Trade and Commerce Co in Pingyi county on Dec 25.

The four, who were spotted by life detection systems on Dec 30, had been provided with food and water. Eleven other survivors were rescued within a day of the accident occurring.

As of Sunday, one worker was confirmed to have died in the collapse and 13 had not been located.

Zhang Shuping, the mayor of Linyi, the city that governs Pinyi, said: “We have never given up search and rescue efforts for the missing 13. We are organizing experts to come up with new rescue solutions.”

Zhang said the authorities will inspect all 212 non-coal mining companies in the city and ban those with safety risks from operating.