WALNUT CREEK (CBS SF) — Firefighters in Walnut Creek have knocked down a two-alarm fire at a senior facility in the Castle Hill neighborhood Thursday afternoon, according to authorities.

The Walnut Creek Police Department sent out an alert shortly after 4 p.m. warning of a large structure fire burning in the area of Castle Hill Road not far from the freeway, the Rudgear Road/South Main Street 680 exit and Creekside Drive.

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Fire and police units responded to the large structure fire near the I-680 freeway, authorities said.

Walnut Creek resident Bernadette Burns, who lives nearby, described what she heard and saw.

“There were two giant explosions, carried on with two small explosions. So when I looked out my French doors, you could see everything go up in smoke,” said Burns. “It was all black. Everything was pitch black. And then, all of a sudden, a giant fire coming out after that. And I ran down the hill because it is a care facility with seven patients living there.”

“There was a very nice gentleman who went in there and he carried one of them [the seniors], and he was a big guy and he brought him out,” said another neighbor.

Other residents in the area also reported hearing and feeling the explosions on social media. The concussion from the larger explosions was enough to shake homes a half a mile away.

The Contra Costa Fire Department Twitter account posted a photo with details about the fire.

Contra Costa Fire confirmed that the two-alarm fire was burning at a senior care facility in the 1500 block of Castle Hill. All residents were accounted for and being transported to a safe location.

A separate fire across the freeway in the balcony of an apartment on Creekside Drive caused by windblown embers was also extinguished, fire officials said.

Fire officials later said embers started spot fires at three nearby properties, but all three were extinguished without damage thanks to rapid response by fire crews.

In a tweet at 6:45 p.m., fire officials said the fire was extinguished and mop up at the scene was complete. The seniors who lived at the facility have been relocated, Contra Costa Fire said.

The cause of the initial fire is under investigation.

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Smoke from the fire was significant enough to cause traffic delays near the Highway 24/I-680 interchange.