OAKLAND -- Oakland firefighters battled a three-alarm blaze early Friday that broke out in an abandoned residential hotel and sent flames soaring into the pre-dawn skies.

Fire Capt. Melinda Drayton said the fire, which ignited at 2505 San Pablo Ave., was first reported at 1:05 a.m. and jumped to three alarms at 1:11 a.m.

"My brother and I were working (next door)," Michael Sanders told KTVU. "I smelled something suspicious. I went outside and saw a lot of smoke…I walked around to the side of the building and there was an enormous fire coming out of the first floor."

Arriving firefighters were concerned that squatters or the homeless were staying in the building so they immediately broke out their thermal imaging equipment to make sure no one was inside the building.

The fire was under control in about an hour, but was considered suspicious.

"It’s suspicious because there are no real reasons for a fire to start," said Battalion Chief Lorenzo Frediani. "No one is living there. There is no electricity. We shouldn't have a fire in an abandoned building."

One firefighter sustained minor injuries to his hand and was treated at the scene, according to Drayton. No other injuries were reported.

It was the second time this year a fire has damaged the building this year. A three-alarm fire on May 12 that was electrical in nature forced residences out of the building. It had been abandoned and boarded up since that blaze.