Dunedin police are appealing for the return of a tear gas canister and cartridges, which were dropped during a raid by armed officers.



Police believe a black backpack containing a canister and a number of cartridges fell out of an open police car door while officers and members of the armed offender squad were attending a callout last week.



A 30-year-old man barricaded himself inside a house with a running chainsaw on Thursday evening.



The man was eventually arrested and charged with assault after more than six hours were spent negotiating with him.



Dunedin Clutha Area Commander Inspector Greg Sparrow said anyone who might have picked up the bag should not tamper with it.



"This is a rare event and our main concern is for the safety of members of the public," he said.



"That's why we are keen to locate this bag and its contents as soon as possible. Our main concern is that someone finds the canister or the gas cartridges and doesn't know what's in them and tampers with them."



Sparrow said the canister was aluminium and clearly marked in blue writing with the letters CS.



The five missing cartridges looked similar to those used in a shotgun.



Sparrow said an internal investigation was underway to find out how the bag was misplaced.



Anyone who knows the whereabouts of the bag and its contents should call Dunedin police on 03 471-4800 or Crimestoppers on 0800 555 111.