Around 10 flares – some of which are commonly used by marine units and can travel up to 300m in distance – were taken from a garage on Sunderland Road overnight between 9pm on Sunday and 9am on Monday.
Nothing else is believed to have been taken, and officers are now warning the public about the potential dangers of using such devices.
Neighbourhood Sergeant Steve Prested, of Northumbria Police, said: “These flares could potentially be fatal if used in the wrong conditions and could bring serious risk to the public.
“I would urge anybody who is in possession of these items to safely return them to their nearest police station.
"Enquiries are ongoing to trace offenders and bring them to justice.”
Anyone with information should contact police on 101 quoting reference 409 280518.