CONCORD (CBS SF) — Firefighters battled a massive fire early Monday that erupted in a vacant commercial building that formerly was home to Lin’s Buffet near Six Flags Hurricane Harbor in Concord.

Fire officials said they received a 911 call reporting the fire in a building near Willow Pass Rd at Water World at around 2:40 a.m. Arriving fire crews encountered a building engulfed in fire with towering flames roaring out of the roof.

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The building’s windows were boarded up.

“We opened the windows up, there was extensive fire in the building, so it had a good start on us,” said Contra Costa Fire Protection District Battalion Chief Dominic Ciotola. “It was through the roof when we got here.”

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Additional resources were called in. At the height of the firefight there were 4 ladder trucks dumping hundreds of gallons of water on the blaze.

The intensity of the fire forced firefighters to take a defensive approach to battling the blaze. It took about an hour to knock down the flames.

There were no injuries reported and a cause remained under investigation. Ciotola said transients have been living inside the building.

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“The structure did not have gas or electric and it was completely boarded up,” he said.