Rescue crews working underground burrowed close to a minibus trapped under tons of earth and rubble following the collapse of a subway station construction site, but were forced to retreat because of unstable ground, officials said.
Aided by dogs sniffing for the passengers, rescuers found the vehicle but turn backed late Sunday because officials feared the ground might again give way, burying them, Sao Paulo state Gov. Jose Serra said.
Authorities then decided to take a different approach to the bus, entombed under rubble and dirt after the concrete walls of a huge hole being excavated for the station fell apart Friday.
But the effort was complicated by large chunks of concrete that prevented rescuers from going deeper into the crater where as many as many as seven people are buried, including four in the minibus.
Witnesses reported the minibus was carrying a driver, fare collector and two passengers when it fell into the crater, said Bruno Davanco, a spokesman for Sao Paulo's subway system. Two pedestrians and a truck driver may also be buried.
"We are working under the assumption that there may be at least seven people trapped underneath the rubble," Davanco said.
Authorities said they still hope to find survivors more than 48 hours after the collapse at the construction site next to one of Sao Paulo's busiest highways.
"It is possible that an air pocket buttressed by a beam or something else may have been created," Col. Joao dos Santos of Sao Paulo's fire department told reporters. "The oxygen in the air pocket could help anyone trapped underneath to survive."
Above the rubble, heavy machinery was being used to remove earth and debris from the hole in an attempt to get to the minibus from above. But workers were moving slowly and carefully to avoid causing another collapse.
Distraught relatives of the missing spent hours at the site, watching the painstaking process drag on.
"I am praying to God for help," Thais Ferreira Gomes, the wife of fare collector Wescley Adriano da Silva, told the Folha de Sao Paulo newspaper. "Only he can do something."
Witnesses said the 40-meter-wide (130-foot-wide) circular hole lined with concrete gave way without warning, creating an 80-meter (260-foot) crater filled with construction debris that swallowed four dump trucks, the AP says.
More than 100 people living near the site were evacuated in fear that a 55-ton crane teetering at the edge of the site might topple over. Several construction workers were hurt after Friday's collapse, but officials said none suffered life-threatening injuries.
The cause of the collapse was under investigation, but the consortium of Brazilian companies building the subway station said in a statement that heavy tropical rains may have contributed to the incident and denied negligence was a factor.