Police are searching for two offenders involved in a string of 10 armed robberies on taxi drivers across Melbourne’s north-western suburbs.

Detectives believe the offenders request a taxi to attend a random residential address on the pretext of being driven to Tullamarine Airport.

The pick-up areas chosen are usually residential courts or dead end streets with access to a park.

Upon the arrival of a taxi, the offenders will approach from behind and threaten the driver with a firearm or possibly a knife before taking mobile phones and cash.

Police believe since July 2011, the offenders have committed the following armed and attempted armed robberies:

 20 July, Hamel Street, Albion;
 22 July, Derrimut Street, Albion;
 10 August, Hayden Crescent, Albion;
 11 August, Gail Court, Albion;
 28 August, Churchill Avenue, Tullamarine;
 31 August Baxter Close, Gladstone Park;
 2 September, Clarks Road, East Keilor;
 13 September, Thea Court, Keilor Park;
 17 September, Michelin Street, Tullamarine; and
 21 September, Epson Street South, Altona Meadows.

In each incident, both offenders wore dark clothing and balaclavas and removed the taxi ignition keys before fleeing the scene in an unknown vehicle.