Colombian crews resumed efforts Thursday to rescue at least 15 workers trapped in a mine collapse, as authorities launched an investigation into the owners of the unlicensed gold mine.

Rescuers were pumping out water from inside the tunnels in the morning after suspending work at nightfall, and it may take several days to reach the workers, officials at the national mining agency said.

The workers are believed to be trapped at a depth of 17 meters (55 feet) and 10 meters.

The collapse Wednesday at the informal mine on an indigenous reservation in the municipality of Riosucio occurred in its deep shafts, authorities said.

The head of The National Mining Agency told Radio Blu the organization would investigate the mine that was in the process of legalization, but was prohibited from digging the shafts that were involved in the collapse.

Investigators say a power cut in the area likely shut off the mine's water pumps, flooding the shafts and leading to the collapse.

The workers at the artisanal gold mine had no formal contract with the company for their high-risk work, the mining agency said in a statement.

Colombia is a major gold producer and business has boomed over the past decade as the price of gold has risen from less than $400 per ounce to almost $1,200.