Cops are used to surprises on the job, but seldom a casual great white shark.

South Australian Police looking to breathalyse and check up on boat operators last Friday were greeted by the animal, who cruised around them for about 10 minutes.

It's estimated the shark, nicknamed Noah by police, measured around 4.5 to five metres (14 feet) long.

"I told the boys to back off a bit because the shark was right next to us," fisherman Mark Oaks told ABC News.

"For probably the next 10 or 15 minutes we just sat around. The police brought the big boat in, which is where the footage from above the shark has come from."

"Noah wasn't keen on being breath tested and our Water Operations Unit officers were happy to oblige!" South Australia Police wrote in a Facebook post.

The great white shark is arguably one of the most feared species in Australian waters due to its threat to humans. It is listed as vulnerable by the IUCN, however its exact population in the south-west of Australia remains unknown despite attempts to calculate it.