Fishermen have captured dramatic video of a monster great white shark attacking their fishing boat off Victoria's coast. Courtesy Channel Seven news

MELBOURNE fishermen have captured the moment a monster 5m great white shark attacked their tiny fishing boat off Victoria's coast.

The three fishermen, brothers Andrew and Ben Donegan and friend Joel Ryan, were tuna fishing at Cape Nelson, off Portland, near the Victorian and South Australian border, when the huge predator started to circle the vessel.

They said it then suddenly became aggressive and tried to take a bite out of the boat.

The anglers said they may have pushed their luck with the shark, trying to touch it as it circled.

"Every time we put the camera in the water it tried to bite the camera. We've still got our arms and hands, so that's OK," Andrew Donegan said.

"I had just dared Joel to swim out to a buoy when it came up, it was pretty lucky. We thought it was a big mako shark then we realised we were looking at half a tonne of great white shark. It was having a look at us."

The shark became agitated at the attention and took a bite at the boat's propeller. Experts said it may have been attracted to the electrical pulses from the boat's motor.

Mr Donegan said the myth of deterring a shark by punching its nose would not have worked.

"This thing was not even fazed in the slightest. It chewed a moving propeller," he said.

They decided to gun the boat to shore and the shark gave chase.

"We decided to punch it to shore, we thought if this thing jumps or puts its head in the boat we would capsize," he said.

But still they were thrilled at the close encounter, which happened on Saturday, saying they had never seen anything like it.