A volunteer worker at a Southland op shop thought it was just another donation left at the door.

Instead, the bag contained more than 40g, of cannabis, thousands of dollars in cash — and two teenagers who soon returned looking for it.

Police were called and within minutes had detained the pair, uncovering drugs, a weapon, a scanner and more than $4500 in cash linked to alleged illegal activity.

Police revealed today that on February 18, a volunteer at an op shop in Southland noticed the bag at the front door.

“Nothing unusual there. Donations are often left in that very spot for staff to sort through and tidy up for sale,” said a spokesperson.

“However, when the shop worker took the bag inside, they noticed that this particular donation had a distinctive pungent aroma. Once it was opened, it quickly emerged why.”

A number of bags of cannabis, as well as a large wad of cash, were visible inside.

The worker immediately called the police.

“As this was happening, a pair of youths walked into the store, highly agitated, looking for a bag they’d misplaced,” said the spokesperson.

More items of interest were found in the reluctant donors' vehicle. Photo / Police

“Thankfully, local police were extremely quick to respond, arriving on the scene to de-escalate the pair, who were becoming increasingly aggressive with shop staff.”

The youths were detained under the Search and Surveillance Act and police discovered 43.2g of cannabis, scales, other ziplock bags and $3700 in cash in the bag.

“As it transpired, the pair had left the bag out the front of the store while they waited for their car to be serviced at a workshop nearby,” said the spokesperson.

“This led the attending staff straight to the vehicle for another search.

“Inside they located an air pistol and a police scanner. There was also a further $810.”

Police found 43.2g of cannabis, scales, other ziplock bags and $3700 in cash in a bag left at a Southland op shop. Photo / Police

A 16-year-old male and a 16-year-old female were arrested and taken to a police station.

“The quick and calm actions of the shop’s staff allowed for a rapid response from the police and a great outcome in recovering drugs, a weapon, a scanner, and a total of $4510 from illegal activity,” the spokesperson noted.

“Not a bad day at the shop.”