As many as 100 rescuers on Thursday resumed the search for 15 gold miners missing feared dead after the underground shafts where they were digging flooded.
Authorities said Wednesday's accident was likely triggered by a power outage or an explosion more than 14 meters (about 50 feet) underground in the mine located near the town of Riosucio, in northwestern Colombia.
President Juan Manuel Santos called on rescuers to "spare no effort'' in the search and all through the night, crews used pumps to remove 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," Jaime Gallego, a civil defense worker, told The Associated Press from the scene of the tragedy.
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 that preliminary accounts from the site raised questions about whether the mine was complying with safety protocols.
The Nation's Ombudsman 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 seeking government authorization.