Two women, both 21, suffered minor injuries early this morning in Waikiki when a 30-year-old man allegedly robbed one of the women and injured both of them, police said.

The suspect used an unidentified “dangerous instrument” to allegedly rob one of the women at 12:55 a.m. today, police said. Her friend tried to intervene and was assaulted, police said.

An unidentified good Samaritan then detained the suspect until police arrived and arrested him.

The women were taken to a hospital where they were treated for minor injuries.

The suspect was arrested on suspicion of first-degree robbery and third-degree assault. He remained in custody as of this morning.