Istanbul, Turkey (CNN) -- The desperate effort to save 30 miners who have been trapped in a northern Turkish coal mine suffered a setback Wednesday, when officials announced that rescue workers had encountered rubble separating them from the victims.
The head of Turkey's state coal company said it could take four more days to cut through the 20-meter, or 65-foot-long, pile of rubble.
Thirty miners have been trapped 540 meters, or more than 1,770 feet, underground in a massive state-run coal mine near the Black Sea port of Zonguldak since Monday, when a mysterious explosion rocked the complex. Since then, rescue workers say, they have had no communication with the miners.
The rescue effort has been complicated by the fact that one of the elevators running down to the lower shafts was damaged by the explosion. Another elevator only reaches to a depth of 510 meters, or more than 1,670 feet. About 400 rescue workers are on the scene.
But an official from the Zonguldak governor's office, who spoke from the coal mine on condition of anonymity, said that rescue teams were forced to work by hand, without heavy machinery, in a constricted area that only allowed teams of 10 to 15 workers to operate at a time.
Scuffles broke out between police, protesters and distraught relatives of the trapped miners Wednesday, when Turkish Prime Minister Recep Tayyip Erdogan paid a visit to the scene. Relatives have been holding an anguished vigil in a tent near the mine.
On Wednesday, the office of the Turkish president issued a statement on his website, calling for an investigation into the cause of the explosion.
"Our president instructed the State Inspection Council to start research and investigation into the accidents that happened in the mining sector during the recent period that caused casualties and injuries and deeply affected the public," the statement read.
This is the third major accident to shake Turkey's mining industry. Nineteen miners died when a methane gas explosion rocked a mine in the western province of Bursa in December. In February, 13 miners died after a similar explosion hit a mine in Balikesir.