BOSTON (CBS) — Two people were injured, one critically, when a concrete facade collapsed on Harvard Avenue in Boston Sunday afternoon.

First responders rushed to the scene in front of the Common Ground restaurant just before 3 p.m. Deputy Fire Chief Steve McNeil said a parapet wall above a facade along 75-85 Harvard Ave. came crashing down, sending parts of the building onto the sidewalk below.

The incident sent two people to the hospital, including one person who suffered critical injuries.

Authorities are looking for anyone who may have witnessed the incident.

A sign for Common Ground could be seen in the rubble.

The sign for Common Ground fell during the facade collapse (Photo credit: Jim Smith/WBZ-TV)

One witness told WBZ-TV that a woman struck by falling debris was bleeding and appeared to be badly injured. Some people tried to get her out from underneath the rubble and performed CPR, he said.

“She was unresponsive,” said Jonathan Aguirre, who called 911.

Six people inside the building were safely evacuated.

“In many ways it’s amazing that there weren’t more injuries given what occurred,” McNeil said.

The cause of the collapse isn’t yet known. McNeil said it didn’t appear there was any construction work going on in the area at the time.

Harvard Avenue was closed between Brighton Avenue and Cambridge Street, as McNeil said there is “significant danger” of a secondary collapse.

Crews tore down more of the building Sunday night before anything else could fall on its own.

Crews work on the collapsed facade Sunday night. (WBZ-TV)

“We have to see how far that collapse caused damage to the primary structure of the building,” Inspectional Services Commissioner Buddy Christopher said. “Right now we’re very comfortable that we’ve stabilized the building for the night but we’ll be back here early tomorrow morning to do our forensic analysis.”