(CNN) -- Rescue workers searched Friday for four miners believed trapped in a collapsed mine in southern Ecuador, a government official said.

The miners have been trapped since about 3 a.m., said Jorge Espinosa, the under-secretary of mining development at Ecuador's Ministry of Nonrenewable Natural Resources. They are about 500 feet (150 meters) deep.

At least 50 rescuers were working Friday afternoon to try to free the four, Espinosa said. Authorities do not know the miners' condition because they have been unable to make contact with them, he said.

The gold mine, which officials say is owned by Minesadco, is near the town of Portovelo, near Ecuador's southern border with Peru.

"We are working on two plans to rescue them and we are expecting to reach them in 20 to 24 hours," said Espinosa. "We estimate that there are about 30 cubic meters of air so we believe the miners would be able to breath for five or six days. The problem is that we don't know if the area of the mine where they were working was also filled with mud."

The incident comes two days after crews in Chile rescued 33 miners who were trapped underground for 69 days in a stunning rescue operation, watched by the world.