Honolulu police arrested a 23-year-old man after he allegedly entered a women’s bathroom at Ala Moana Center and punched a 20-year-old woman in the face Monday.

Police said the assault occurred at about 3:20 p.m. The suspect and victim are not known to one another.

Witnesses and security personnel detained the suspect until police arrived and arrested him on suspicion of second-degree assault and third-degree assault.

The victim sustained “substantial bodily injury” in the assault and was treated at a hospital, according to police.