Up to 300 other workers are believed to be trapped underground at the mine in Soma, Manisa province.
Those trapped are about 2km (1.2 miles) below the surface and 4km from the mine's exit.
Search and rescue operations are taking place. It is estimated that 580 workers were underground at the time, but that many escaped.
Quoting health officials, local MP Muzaffer Yurttas told broadcaster NTV that 20 bodies had been retrieved and that at least another 20 workers had been taken to hospital. He said later that four people had been killed.
"They died of choking and burns," he said.