A woman has been charged after a teenage girl was robbed and taken into a police station at knifepoint.

The 16-year-old girl had just got off her school bus and was waiting for her parents outside the Bass Hill police station about 4pm on Tuesday, police said.

An 18-year-old woman then approached the girl, allegedly threatening her with a knife and demanding the girl’s mobile phone.

The girl, who did not know the woman, handed over her phone but the woman allegedly pushed her to the ground.

The woman then picked the girl up, and walked her into the police station holding the knife to the girl’s throat, police allege.

An officer on duty called for urgent assistance before negotiating with the woman to drop her knife and let the girl go.

The senior constable arrested the woman, and she has been charged with a number of offences including armed robbery, kidnap, and assault occasioning actual bodily harm.

Refused bail, the woman will appear at Bankstown Local Court on Wednesday.