As anguished relatives looked on from behind a security perimeter 24 hours after the tragedy in western Colombia, six backhoes clawed at the earth to try to get to the missing.
Both men and women are among the missing, said Alexander Sanchez of the Red Cross in western Cauca state, who revised the initial missing toll of 30.
"It will be hard to find survivors," Sanchez said.
Cauca police said three bodies had been pulled from the earth.
The number of missing could rise because so far it is based on reports from relatives and others may not yet have come forward.
Widespread illegal mining
Luz Holanda Nazarin, whose nephew was among the missing, said she had given up hope.
"Not even God knows where they are," said Nazarin, aged 50.
Rescue workers were waiting for the heavy machinery to remove enough mud to send in sniffer dogs. But they said lots of earth still had to go before they could do this.
Cauca state firefighters chief Victor Claros said the accident happened at a mine outside the city of Santander de Quilichao, where independent mine workers were digging for gold without a license.
Colombia has more than 14 000 mines, more than half of which operate without proper permits, officials said. The government even has confiscated heavy excavation equipment at some illegal sites.
It was the second mining accident in Colombia in less than a week.
Last Saturday in the northwestern department of Antioquia, four miners died from inhaling toxic gas in an unlicensed mine.
Rebels cashing in
The owners of the mine in the new accident, rather than use their own equipment to try rescue the missing, hid it to keep it from being seized because the mine has no permit, Mining and Energy Minister Amylkar Acosta said.
Justice officials said the mines, illegally scoured for their minerals, pose a risk to the workers who enter them.
"The conditions of informal labor and informal infrastructure pose a latent risk to workers," said a statement released on Thursday by the office of the people's ombudsman, which is tasked with defending the rights and welfare of Colombians.
The office says that FARC leftist rebels, active in western Colombia, cash in on illegal mining by charging to let heavy machinery in to do work.
The National Mining Agency says that from January to September of 2013 there were 66 accidents in Colombian mines, causing 71 deaths and 51 injuries.
In 2012 mining accounted for 2.3 of Colombia's GDP.