TOKYO (AP) _ Anguished relatives fought back tears Thursday after being told they must wait even longer for workers to reach 20 people trapped for more than five days inside a crushed mountain tunnel.

Workers could see a bus flattened to 3 feet high, but large teetering rocks were hampering efforts to reach it.

``I'm so disgusted I have nothing to say,'' Toyomitsu Murakami, 44, told the Kyodo News Service while waiting for word of his 17-year-old daughter, Asami. ``I want to bring her out of that dark, cold place.''

There was almost no hope of finding survivors in the freezing cold.

The bus, with 19 people inside, was flattened when a rock the size of a 20-story building peeled off the mountainside Saturday and smashed through the tunnel roof. A car also was trapped.

An explosion Wednesday finally broke up the huge boulder after three unsuccessful attempts, but several large rocks threatening to topple were hampering efforts, said Makoto Niiyama, a rescue official.

Digging from the other end of the tunnel could take through Saturday, he said.

Anxious relatives kept vigil at the tunnel, about 550 miles north of Tokyo outside a remote fishing village on the northern island of Hokkaido.

The troubled rescue effort _ which has been criticized by some as slow, ineffective and secretive _ has dominated national news coverage, with frequent live television updates.

More than 100 trucks, backhoes and bulldozers have been sent to the scene, along with several hundred soldiers and police. Ambulances waited near the tunnel's mouth.

In a flurry of snow, power shovels worked through the night, clawing at the mountainside. Trucks carried away piles of rocks and debris.

Rescue officials said they would work continuously, using crews in shifts. A biting wind and swirling snow added to difficult conditions at the seaside site.

Also hampering efforts was poor air quality inside the tunnel, the result of chemical residue from the explosions and exhaust from emergency vehicles.

A human arm was seen through a fiberscope _ a tiny camera in a fiber optic tube _ inserted through the rubble Sunday, but there was no indication of the person's condition and no new discoveries Thursday, police said.

It was not clear why the rock fell. Water may have frozen in cracks in the mountainside, loosening the rock, experts said. A boulder twice the size plunged from a nearby mountainside 18 months ago but did not hit a roadway.