PORTLAND, Ore. (KOIN) – A Southwest Portland apartment building started to collapse on Wednesday after a four-alarm fire ripped through the structure on Tuesday.

The start of the collapse comes after crews said they extinguished the last hot spot earlier in the day.

Doug Keller with Paul Davis Restoration was already at the site Wednesday afternoon, waiting for their crew to get fencing up in the area to keep folks out as part of the wall crumbled.

“I was waiting next to my truck here, and all of a sudden, I heard a bang and turned my head toward the building and saw layers of brick just folding over the side hitting the sidewalk and little bricks hitting the road and bouncing,” Keller said.

During a 3 p.m. Portland Fire & Rescue press conference, Public Information Officer Rick Graves said “this building is of imminent concern to collapse. This is an unreinforced masonry building that was effectively being held together by the floors.”

PF&R tweeted at 10:43 a.m. Tuesday that crews were at the scene of the blaze on Southwest 14th Avenue and Southwest Taylor Street. When firefighters arrived, there was heavy fire coming from the third floor and extending to the fourth floor.

Officials said they were concerned that the fire could cause the building to collapse on Tuesday and temporarily closed Interstate 405, which has since reopened.

According to Graves, the apartment building has been evaluated by a city engineer and was “red-tagged,” which prevents civilian entry moving forward. Graves said the building housed 42 units and about 100 residents.

Fire crews were able to save two buildings and escorted residents to their apartments one at a time for a maximum of five minutes to gather personal belongings, Graves said.

“These floors are now extremely damaged and affected by fire, flame and water. So, there’s a heavy concern, or a significant concern, we could lose this building at any time. In fact, when we’re just blowing water gently on one side of the building, we make sure everybody on the other side of the building is away. It’s that perilous,” Graves said.

During Wednesday’s press conference, officials said a forensic investigation will begin on Friday with drone assistance from fire officials in Scappoose.

If needed during the investigation, Graves said the city engineer has permitted a firefighter to enter the building with a rescue crew nearby as they investigate the cause of the fire.

“If it is determined that it is a threat to the safety of the community and the safety of citizens, an encouraging process needs to go through to have the building taken down,” Graves said — noting nearby streets are expected to be closed off until Saturday.

According to Graves, no cause for the fire has been ruled out and said “everything’s on the table” as they investigate.

Two firefighters were injured during the incident. One continued to work and the other was taken to the hospital after experiencing high blood pressure and has since been released.

Graves said the Red Cross has opened a shelter for displaced residents at University of Portland.

Portland police say they’ve responded to the complex 14 times and Portland fire crews have responded 28 times — all in just the last year.

There are four verified GoFundMe fundraisers that aim to help those who have been displaced by this fire:

Watch the full press conference in the video above.