A large, fast-moving fire caused a partial collapse at an apartment building in Squirrel Hill on Tuesday morning.

The fire started around 8:20 a.m. on Forward Avenue, prompting a massive response from Pittsburgh firefighters and other city first responders. Heavy smoke and flames could be seen billowing from the building, which is nearly 100 years old. Smoke was visible from the nearby Parkway East. 

Everyone who lived in the building was accounted for, and no one was injured, Public Safety said. The fire was finally declared under control shortly after 1 p.m. 

Crews battle challenging fire

Around 10 a.m., the intense blaze caused a large portion of the roof to collapse, as well as part of the front of the building. Firefighters were just outside when the collapse happened, but the façade fell backward in the other direction. 

The fire may have started in a kitchen on the third floor of the building and then spread across the roof, quickly growing out of control. However, authorities are still investigating. 

Pittsburgh Fire Chief Darryl Jones said 73 firefighters were on duty at one point, battling the four-alarm fire.

"There was one [firewall], but it was defeated. So it was going across from right to left as you face the building. The firewall was going from front to back in one wing of the building. The roof is burned off the building," he said. 

A reported electrical fire in the basement of the building may have complicated the fight further. 

Because of the collapses, crews were ordered out of the structure. They moved to using aerial trucks with ladders to fight the fire. 

Jones said it required patience to keep any firefighters from getting hurt. 

"This is just one of those ones that we have to be patient, and because of the partial collapse, we have to consider that the whole building is suspect now," he said. "I can't send my guys in and all that water you see going in is weight —that's tons and tons of water, a live load that we put into this building that this building was not designed to hold."

Evacuated residents watch devastating blaze

Firefighters went door-to-door to alert the people living there to the fire, telling them they needed to get out. Still in their robes and pajamas after being evacuated, residents watched in horror as flames destroyed their building. 

"It's kind of surreal, honestly. I wasn't on the third floor, like I said, so I wasn't in immediate danger but seeing them work on it, and then seeing it look like it calmed down for a bit and then flare up, then suddenly the roof collapsed. It's a lot to take in all at once," one resident said.

There are 44 units in the building and about 30 of them were occupied. Many of the residents are worried about the pets they had to leave behind in the building. Public Safety said firefighters were able to save two cats from the building, but a third was found dead. 

Resident Matthew Stock said the fire spread quickly and without warning. 

"I thought someone burned their breakfast or something, so I opened the window to let the smoke out, and next thing I know, there's firefighters going up the stairs. They're banging on the doors letting everyone know they've got to get out," Stock said. "At first they had it contained, and then it started to spread. We saw more black smoke coming up, and then without warning, we just had these sudden flares of fire and then the roof collapses in, which was pretty dramatic as you can imagine."

The Red Cross and Salvation Army responded to the scene to help. The Red Cross opened an emergency shelter for all those who lost their homes in the fire. It is located at the Greenfield Recreation Center on Greenfield Avenue.

"We have our Office of Emergency Management and the Red Cross from Pennsylvania and the Salvation Army — all three groups working together to get them some immediate necessities," Cara Cruz of Pittsburgh Public Safety said. "Get them to the Jewish Community Center, and also work from there on getting them some temporary accommodations because, quite clearly, you can see behind me this building is not going to be habitable."

Smoke could be seen for miles 

The fire's impact stretched beyond the building. The entrance ramp to the inbound Parkway East was closed, and the inbound side of the Parkway was moving slowly. Officials also had to monitor the air intake for the Squirrel Hill Tunnel, as the fire could have impacted the air quality in the tunnel's supply.

The smoke could be seen from miles. 

"I walk to school every morning and it was just really hazy, like I just thought it was fog," said Pitt student Tal Newman.

You could see it from I-376 before the Squirrel Hill exit as well as on the other side of the tunnel. 

"I was driving in from Robinson, getting off the Parkway. It was all blocked off in Squirrel Hill," said Jude Corasaniti. "It was my concern because you could see the smoke was crazy coming up, you could see it for some miles. I'd probably say two miles."

People like Diane Garrett woke up to the smoke. 

"The smoke was almost over our neighborhood," Garrett said.

"You could see it everywhere. They were showing it from Mt. Washington, my friend in Monroeville, she said she could see the smoke," Garrett added. 

The fire is under investigation.