A fishing expedition in Auckland's Hauraki Gulf was stalked by a great white shark.

Footage of the close encounter shows the shark circling the fishing boat near Kawau Island on Saturday before opening its jaws for a taste of the outboard motor.

The three men on board the boat, Jack Lucas, Adam Ellington and Chris Pom, were out on Saturday looking to catch some king fish and surprised to see the shark.

They said it stalked the boat for about 20 minutes before it "attacked". In the video you can hear one of the men saying how angry the shark looks.

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Department of Conservation marine scientist Clinton Duffy said the shark wasn't "attacking" the outboard, but mouthing it to see if it was edible.

"The shark has obviously been attracted by the fishing activity, and possibly the scent of berley or bait dripping into the water off the transom."

Mr Duffy said it was very common for sharks to mouth outboard motors like this, and it was believed they did this because of the weak electric field created by metal in seawater, called electrolysis.

"The ampullae in sharks' snouts are very sensitive to weak electric fields given off by prey and its possible this is why they are attracted to metal objects like outboards and anodes bolted to vessels hulls.

"It could of course be that they're just objects sticking out of the back of something that smells like it may be edible."

The small great white was one of three great whites seen in the Hauraki Gulf since May 9.

Sharks are common visitors to waters off Auckland. In January a 4m great white shark leaped out of the water in Waitemata Harbour, scaring family on a fishing trip.