CONCORD (CBS SF) — A two-alarm fire swept through a vacant building at a church complex in Concord early Thursday morning, according to fire officials.

The fire was burning on the grounds of Christ Community Church of the Nazarene at 1650 Ashbury Drive. Fire crews arrived at around 5:30 a.m. to find a two-story building consumed by flames.

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The building, on the opposite side of the complex from the main church, was severely damaged in the fire that burned through the roof. The sanctuary and church offices were not affected.

The first arriving crews found heavy flames coming from the two-story building.

“They attempted to make an interior attack in the first 10 or 15 minutes, said Assistant Fire Chief Jeff Peter. “They had to back out to a defensive fire attack just due to safety issues as the fire had too much hold on the building.”

Crews eventually extinguishing it by about 6:15 a.m. and saving an adjoining one-story building from burning, Peter said. No injuries were reported as a result of the fire, and its cause remains under investigation.

Concord police said areas of Ashbury Drive, near Clayton Road, were shut down and urged people to stay out of the area.

An overnight security guard who was sleeping at the complex said the building, once used for classrooms, was vacant at the time of the fire. John Olveira told KPIX 5 the church has had problems with squatters inside the abandoned property and he has frequently had to chase them out.

“Now it’s been abandoned, but we’ve got a lot of problems [with] homeless and vagrants coming in. They’re making themselves at home.” he said.

Head Pastor Janelle Maher said the church had recently sold the property and are in the process of moving. She was not too upset about the fire, but expressed concerns for anyone who might have been inside.

“My only concern is that that person would be okay and got out safely,” Maher said. “There’s nothing to be angry about. I would just want people to be okay.”

The new owners are converting the property into affordable housing.

Firefighters were able to save the rest of the church, including the sanctuary.

“I mean, we thank God for everything. That’s just kind of who we are,” explained Maher. “But we also don’t necessarily believe that God only intervenes on our behalf. Sometimes it’s just the way life is.”

Kiet Do contributed to this story.

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