Police are investigating a series of knife-point robberies on taxi drivers in Oldham.
Inspector Alan Humphries from Oldham Neighbourhood Policing Team said: "We have seen numerous acts of violence and anti social behaviour directed against taxi drivers in Oldham.
"These offences are being given the highest priority and are being investigated thoroughly. We continue to work closely with taxi companies, Oldham Council and other partners to investigate and put a stop to further offences.
"It is not right that these people should be threatened in this manner and these offences will not be tolerated. They provide a valuable public service and they do not deserve this treatment."
Police have so far made six arrests. There are currently four on police bail pending further enquiries and two in custody for questioning.