Teenagers fled down live railway tracks after snatching mobile phones from a branch of Carphone Warehouse this morning.
Transport for London suspended services on the Northern Line between Camden Town and Edgware after three boys ran down the southbound Tube tracks at Golders Green after the theft.
Witnesses said five boys, believed to be in their teens, ran in to Carphone Warehouse at the corner of Golders Green Road and Finchley Road and snatched up to ten mobile handsets at about 11.30am.
The store is believed to display real handsets as opposed to replicas found in other mobile phone shops.
One eye witness said he saw the gang running across the road towards the station after the robbery, ripping security badges off the handsets.
The group are believed to have split up, with two running north up Finchley Road while three more fled into Golders Green station before jumping the barrier and sprinting off down the live tracks.
Transport for London cut the power supply to the rails and British Transport Police says its officers have carried out extensive searches but have not found the suspects.
Stations reopened on the Northern Line and services were resumed at 2.10pm but Carphone Warehouse remained closed this afternoon under police guard.
The incident mirrors another robbery at Carphone Warehouse branch in Station Road, Edgware on Monday.
Two 15-year-olds were arrested in that incident after a gang of six teenagers ran into the store and snatched phones and a Notebook laptop.