At least 15 people were trapped underground Wednesday when an unlicensed gold mine in western Colombia collapsed, authorities said, as rescue workers raced to reach them.

"A mine collapsed, apparently after flooding caused by the holes drilled to extract the mineral. At least 15 people are trapped," said Luis Pineros of emergency response agency UNGRD.

"We're in the middle of search and rescue operations," he told AFP.

The accident happened on an indigenous reserve in the municipality of Riosucio.

Some of the miners are trapped at a depth of about 17 meters (55 feet), others at about 10 meters, said the police commander for the department of Caldas, Luis Duarte.

The National Mining Agency (ANM) said local firefighters reported that gases in the deep, vertical tunnels likely contributed to the cave-in.