A 23-year-old man from the mainland was arrested last night after he allegedly punched and knocked out his girlfriend in the elevator of a Waikiki hotel, then left her there unconscious.

The woman, 22, told police she was arguing with her boyfriend before he hit her about 7 p.m.

Police said hotel security workers found the woman in the elevator. She was taken to a nearby hospital where she regained consciousness, police said.

The boyfriend was arrested without incident at 2005 Kalia Road on suspicion of second-degree assault.