Rescue crews on Tuesday suspended their three-day effort to reach a minibus entombed 300 feet underground, fearing the unstable earth around a collapsed subway construction site could give way again.

The decision outraged relatives of at least four people inside the minibus, but authorities said they had no choice.

"We've reached the limit, we have to stop," said Marcio Pellegrino, a spokesman for the consortium of Brazilian companies building the subway line in a heavily developed part of Sao Paulo, South America's largest city.

Workers sprayed concrete on the dirt walls of the crater to strengthen but authorities said it could be days before the search resumes.

On Monday rescuers found the bodies of two women buried in the crater, which was created when the walls of the huge hole being excavated for the station collapsed on Friday. Five more people were missing, but hope that anyone else could still be alive was almost nonexistent, officials said.

Rescue crews first found the body of Abigail Rossi de Azevedo, 75, who was walking near the site when its concrete walls collapsed. Several hours later they spotted the body of an unidentified woman inside the minibus but did not remove her.

Three other people were believed to have been inside the minibus, while pedestrian and a truck driver were also feared buried.

"The possibility of finding survivors after a tragedy like this is what motivates rescue workers," Sao Paulo Civil Defense Coordinator Jair Paca de Lima told The Associated Press. "But unfortunately I have to say that the chances of finding survivors is minimal."

Witnesses reported the minibus was carrying a driver, fare collector and two passengers when it fell into the crater.

Construction companies said unusually heavy rains played a major role the collapse. But Sao Paulo state's deputy governor, Alberto Goldman, said Monday he believed a "major engineering flaw" also helped produce the gaping crater that swallowed dump trucks, ripped apart subterranean concrete walls and damaged several homes.

"This was without a doubt one of the worst accidents of its kind in the history of Sao Paulo," Lima said. "Before becoming civil defense coordinator I was firefighter for 30 years during which I never saw something like this."

Witnesses said the 130-foot-wide circular hole lined with concrete gave way without warning, injuring several construction workers. More than 100 people living near the site were evacuated.

The union representing subway construction workers said at least 10 other accidents have occurred in construction of the new subway line, but Friday's collapse was the worst in the system's 32-year history.

The station is one of 11 being built along the subway system's new 8-mile "Yellow Line," a $1.4 billion project expected to be concluded in 2012.