Major Perry Covington, director of public affairs at the base, says the pilot ejected before the crash on Thursday and was not hurt, agencies reported.
Images and videos on social media show a large hole in the roof of the building east of Los Angeles. Covington says there are no injuries on the ground.
Officials say the plane is assigned to the Air National Guard. Interstate 215, which runs near the base, is closed in both directions.
The jet slammed into the side of a commercial building off the base, on Van Buren Boulevard, about 3.45 p.m. on Thursday, March Air Reserve Base Deputy Fire Chief Timothy Holliday was quoted as saying.
The Riverside County Sheriff's Department confirmed on Twitter that the crash occurred around Van Buren and the 215 Freeway, Xinhua news agency reported.
"Multiple agencies responding. Please stay out of area and clear emergency vehicles," the department tweeted.
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