Deputies and medics responded to the scene, at 155th and Densmore Avenue North, at about 9 a.m. after receiving a report of an injury accident.
A King County Sheriff's spokesman at the scene said a man in his 50s was headed east in his electric wheelchair in the bike lane when a VW Jetta traveling in the same direction drifted into the bike lane and sideswiped the wheelchair.
The person in the wheelchair sustained a fractured leg and possibly other injuries. He was taken to Harborview Medical Center and is listed in serious condition.
The driver of the Jetta, a woman in her 60s, was on her way to work at the time of the accident. She was uninjured.
The collision is under investigation.