Crews are worried that some of the building will tumble. A five-story-high scaffold collapsed in just ten seconds, crushing four parked cars.
"We do anticipate potentially further wall collapses. At this point we are in defensive operations," said Concord Fire Chief Terence Carey.
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This was one of the largest fires in Concord's recent history.
It moved fast, tearing through the mostly wood framed apartment building which was set to open later this year.
All those living in Renaissance Square Apartments across the street ran for their lives. Hot embers and ash fell from the sky and landed all over their building.
Evacuees were given a few minutes to get inside their homes and pack only the essentials.
As long as the building is unstable, the Renaissance Square Apartments are in jeopardy too.
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Vincent Billbaneo wasn't able to leave with his cats once the fire alarms went off. He's back, determined to get them out. His persistance paid off.
"You're okay, calm down. I know you're scared," he said to one of the cats. "I had to come back for them."
Most evacuees are staying with family or friends though the Red Cross is offering shelter at a nearby church.
Two people were injured in the fire.