Police are trying to establish whether robberies at three Gateshead bookmakers are linked.
At 1035 GMT a man armed with a metal bar demanded money from staff at Ladbrokes, in Coatsworth Road. He grabbed a small amount of cash.
On Sunday afternoon, a man armed with a pool cue threatened staff at Ladbrokes, Saltwell Road, but left with nothing.
On 26 October, a pair armed with a machete and a hammer targeted Front Street, Swalwell.
Det Ch Insp Mark Warcup of Gateshead Area Command said: "We're not ruling out the possibility that the same people are responsible for these three robberies.
"However I'm appealing for help from the public to find the people responsible.
"Thankfully, no-one has been injured, but such incidents can be very traumatic for the staff involved."