Peru's government 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 (eight meters) of collapsed earth and rock blocking the entrance of the mine, whose horizontal shaft is dug into a mountainside 175 miles (280 kilometers) southeast of Lima. Firefighters have fashioned wooden beams to support the debris removal but their relatively crude efforts prompted Mining Minister Jorge Merino to appeal for help from mining companies. Thursday's collapse occurred following a blast set by the miners themselves in a mine last exploited commercially in the 1980s. Through a hose, 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 though none appear to be hurt. They're being subjected to a lot of cold. The temperature is low because of the humidity," said Prime Minister Oscar Valdes. Valdes told the reporters he estimated the miners would be freed in two to three days and that he had spoken to the men. Miners arrived on Sunday evening from two nearby mines to help dig out the miners, authorities said. The appearance of Valdes and Merino at the Cabeza de Negro mine 4,400 feet (1,347 meters) 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. 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.