A bag and canister similar to those mislaid by police. Supplied photo.

Dunedin police are appealing for help finding a bag containing tear gas that was mislaid by a staff member on Thursday.

"This is a rare event and our main concern is for the safety of members of the public," Dunedin-Clutha Area Commander Inspector Greg Sparrow said today.

Police said the black bag contained a gas cannister and a small number of shotgun-like gas cartridges.

The canister is aluminium and clearly marked in blue writing with the words CS. It does not pose a risk to anyone unless it is opened.

The five missing cartridges look similar to shotgun rounds and should also not be tampered with.

"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."

The bag was mislaid by a police staff member during an incident in Dunedin on Thursday. Although the police had carried out extensive inquiries the bag and its contents had not been found.

An internal investigation is under way to determine how the bag was lost ande to ensure it did not happen again.

"If anyone has located the bag or its contents, they can return to Dunedin Police, no questions asked.

"Alternatively, if anyone has information about the equipment's whereabouts, they can pass the information on to Dunedin Police or anonymously through CrimeStoppers," Insp Sparrow said.