BOGOTA, Colombia (AP) – Search teams worked for a second day Thursday hunting for 15 gold miners missing and feared dead after water poured into the underground shafts where they were digging.

Authorities said Wednesday’s accident at El Tunel mine in the northwestern town of Riosucio was likely triggered by an explosion or power outage that disabled pumps used to extract water and supply oxygen to crews working as deep as 90 feet (27 meters) below ground.

Miner Yeison Gutierrez said he was able to save several colleagues because he was one of the few who knew how to swim. He said one co-worker slipped through his hands and didn’t make it above ground.

“I swam to the surface fighting against the water and the air pressure; that’s how we were saved,” Gutierrez told The Associated Press from the mine where he was assisting the search.

President Juan Manuel Santos called on rescuers to “spare no effort” in the search.

Family members huddled near the mine throughout Wednesday night as crews used pumps to remove the water that raced into three vertical shafts from the adjacent Cauca river. Authorities said it could take at least three days to clear the mine.

“Every hour, every minute and every second that goes by the chances of finding survivors diminishes,” said Jaime Gallego, a civil defense worker.

Mining accidents are common in Colombia but usually take place in wildcat mines dominated by leftist rebels and criminal gangs.

Natalia Gutierrez, the head of National Mining Agency, said the mine that collapsed Wednesday was in the process of being legalized. But she told Caracol television there are questions about whether the mine was complying with safety protocols.

The national ombudsman’s office on Thursday called on authorities to investigate the mine’s owners for negligence and reinforce controls at the estimated 3,000 other semi-illegal mining projects that are seeking government authorization.

Gutierrez, the miner, said workers are paid a percentage of the gold they extract, earnings that range between $400 and $800 a month.