(CNN) -- Nine miners trapped in a flooded coal mine in northwest Colombia are feared dead, police said Thursday.
Colombian rescue workers were fighting against time to find the miners, who were trapped Wednesday afternoon in Angelopolis in the nation's department of Antioquia.
The National Police commander in the area, Mauricio Marin, told reporters Thursday that they had found some of the miners' belongings.
"But it seems the miners are dead," he said.
According to the Colombian Geological Survey (Ingeominas), an accident was reported at the Desespero coal mine.
Ingeominas reported that the mine flooded but did not speculate on the cause. But Colombia's Caracol Radio reported that a subterranean water deposit had ruptured.
Marisela Bustamante, the sister of two of the miners, told CNN affiliate Caracol TV that "it was the first day of work, my two brothers went inside the mine at 2 p.m., and about 10 minutes later, the tragedy occurred."
The only known survivor is Norberto Isaias, a miner who escaped.
He told Caracol TV that "we were working, and a burst of water dragged us all, and I could only save myself. The water dragged all of us, and the mine was flooded."
Ingeominas said in a news release that the mine is illegal. But Arnulfo Velasquez, the owner of the coal mine, says he has all necessary insurance and the mine is not illegal.