A 20-year-old woman attempting help a man seeking directions came in for a rude shock when he robbed her at knife point at Ang Mo Kio on Thursday.

The incident happened at about 9.50pm, when the victim was walking along the pavement of Ang Mo Kio Avenue 6. The 28-year-old suspect approached her to ask for directions, and as she browsed through her handphone, the suspect attempted to grab the phone from her.

The man whipped out a knife after a struggle ensued, and threatened the victim into letting go of her handphone.

Three bystanders who heard the victim's cries for assistance immediately came forward and helped to detain the suspect.

Officers arrived on scene shortly after and placed the suspect under arrest. The victim sustained injuries to her arm and was sent to a hospital for outpatient treatment.

A fruit knife was also found in the suspect's possession. Preliminary police investigations showed that the suspect could also have been involved in another similar case of armed robbery that occurred on the same day in the vicinity of Nanyang Crescent.

A handphone believed to have been taken by the suspect during the crime was recovered.