LIMA, Peru -- Peru's mining minister appealed to mining companies on Sunday for heavy equipment and experts to help free nine miners trapped for four days in an informal copper mine.

Several dozen rescue workers have been using pickaxes and shovels to try to remove the 26 feet of collapsed earth and rock blocking the entrance of the mine, whose horizontal shaft is dug into a mountainside 175 miles southeast of Lima.

Firefighters have fashioned wooden beams to support the debris removal but their relatively crude efforts prompted the appeal by Mining Minister Jorge Merino.

Thursday's collapse occurred following a blast set by the miners themselves in a mine last exploited commercially in the 1980s.

Through a tube, rescuers have been able to communicate with the trapped miners and provide them with liquid sustenance and the local police chief, Jose Saavedra, told The Associated Press that several tons of earth and rock have already been removed from the tunnel's mouth.

Officials worry, however, that some could suffer from exposure.

"They're being subjected to a lot of cold. The temperature is low because of the humidity," said Prime Minister Oscar Valdes. The appearance of Valdes and Merino at the Cabeza de Negro mine 4,400 feet above sea level highlighted what some consider the government's lack of preparation for such an accident.

Peru "doesn't have a specialize team for mining rescues," said Jose de Echave, a former deputy environment minister. Mining is the main engine of Peru's economy, accounting for more than 60 percent of its exports.

It is the world's No. 2 copper exporter after neighboring Chile and ranks sixth in gold exports.

According to official figures, 52 miners died in Peru last year in work-related accidents, a third of them in mine shaft collapses.

By FRANKLIN BRICENO, Associated Press