Two people were in critical condition and one was listed in fair condition Friday as the St. Vincent de Paul homeless shelter across the street from the walkway offered counseling to residents whose friends were injured in the mishap.

Sister Carmel Lohan, the shelter chaplain, said residents were steeled to handle tragedy. Many have estranged family and friends and abused alcohol and drugs.

"The people here are down on their luck and have really touched rock bottom in many ways," she said between counseling sessions. "In adversity they seem to have found strength and faith."

Authorities said the cause of the collapse was unclear.

Investigators will look at whether scaffold above the walkway contributed, said Dean Fryer, a spokesman for the California Division of Occupational Safety and Health. There were reports that workers were dismantling the scaffold at the time.

The scaffold "could have had some impact on the integrity of the walkway," Fryer said. "The bottom line is we have to look at everything."

Fryer said the investigation could take up to six months.

The critically injured were a 50-year-old man and two women, ages 57 and 60, said Maurice Luque, spokesman for the San Diego Fire-Rescue Department.

Scripps Mercy Hospital treated a man and woman in critical condition for injuries including broken bones, said spokeswoman Kristin Reinhardt. UCSD Medical Center was treating a woman in fair condition, said spokeswoman Jackie Carr.

Five people living at the homeless shelter were hospitalized, one with "horrible head injuries," said residential director Julie Vance. The chaplain said about 20 people gathered for prayer in the shelter courtyard Thursday night.

Shelter officials worked to defuse false rumors, including one that a resident died.

"Life and death is pretty fleeting here," said resident Lowell Siwundhla, 55, who shared a bunk bed with one of the seriously injured. "If someone dies on the street, it's just a paragraph in the newspaper."

The shelter is on the edge of downtown, a few blocks from Petco Park, home to baseball's San Diego Padres. It's also a short walk to trendy clubs, stores and new high-rises.

The covered walkway was a favorite hangout for homeless people looking for shade. It lined the 275-unit apartment building under construction by Affirmed Housing Group of San Diego, which is scheduled for completion early next year.

Allgire General Contractors Inc., the Carlsbad company that is overseeing construction, said no workers were injured.

Allgire was fined three times over the last decade for safety violations, according to U.S. Department of Labor records. The largest fine was a $15,750 penalty issued in December 2004 for not having guardrails on an elevated platform or stairway at a work site, Fryer said.