Officials also tell Action News that 80 fire companies from 5 counties helped extinguish the blaze.
The fire broke out at 4:53 p.m., at an unoccupied building at the Riverwalk at Millenium apartments, a $51 million upscale apartment complex. The fire spread rapidly and destroyed the building.
The fire spread to two occupied buildings. It was finally called under control at 10:30 p.m, over five and a half hours later.
In all, five apartment buildings were damaged - three were destoryed. Engineers are assessing the damage of the two additional buildings, but say it is expected that all will be a total loss, in excess of $100-million.
The Red Cross tells Action News 375 people have been displaced.
Hours after it began, the fire continued to burn intensely. Even as hundreds of firefighters fought to bring it under control, they had to call for more help.
"We're calling in additional fire companies from the outskirts of Montgomery County to try and relieve some of our people," Thomas Sullivan of Montgomery County Emergency Management said during the blaze.
At least 20 fire companies helped fight the blaze.
Residents told of harrowing ordeals trying to get out.
"Pretty chaotic; it was pretty serious," resident Matt Davis said.
"They banged on the door, ran out. I lost my cat, couldn't go back," one resident told Action News.
Hundreds of residents, some of them in tears, watched as their homes went down in flames along with just about everything they own.
"I ran out with some photo albums; by the time we went out, there was already soot falling from our buildings," resident Jennifer Stoli said.
Resident Shukla Chandra Kant was only able to take his passport and the clothes on his back.
Each passing minute created more anxiety.
"It's surreal. People are just in shock; they don't know what to do," resident Hope Raitt said.
It was an emotional scene in the haze of smoke.
Residents were in tears.
Many made frantic calls on cell phones.
"It's like it's happening to somebody else; tomorrow, I'll be freaking out," resident Ray Muller said.
The main concern for many was their pets.
The Riverwalk at Millenium allows animals, so many people arrived home from work only to learn their pets may be trapped.
Jeff Batz worried for hours before finally reuniting with his poodle Teddy.
"I feel bad for everyone who lost everything they had," Jeff said.
Another resident, Negin Naraghi, was relieved when she saw firefighters had rescued her dog, Annie.
"Oh my God, I'm so happy right now, but I feel so bad for all the people that lost animals today," Negin said. A number of people like Elyssa Rosenberg did lose their pets.
"I was at work and got a call from some friends, so I came home, and couldn't even see it before I hear that back building is gone," Elyssa told Action News.
Sadly, as the night progressed, the extent of the devastation was realized, unleashing a roller coaster of emotion.
"You see the devastation and it's very upsetting; you see people who are hysterical and you want to comfort them?it's a rollercoaster," resident Denise Painter said.
Displaced residents were bused to the Spring Mill Fire Company.
The Red Cross handed out food and water and began providing temporary shelter.
Dave Tachna says he's lost everything.
"You just hope for the best and unfortunately it is what is, good new is I got everybody out," Dave said.
Officials say the buildings did have firewalls and fire calking; they are still wondering why the flames went up so quickly.
The Red Cross says the apartment complex owner is putting displaced residents in hotels. Action News is told the SPCA is working to find shelter for animals.
An assistance center is being opened Thursday for victims of the fire.
It will be located at the Spring Mill Fire Company at 1210 East Hector Street in Conshohocken from 2:00 to 8:00 p.m.
Residents needing help will need to bring the following information: a contact phone number, Social Security number, annual household gross income, address of the damaged property, and insurance information.