A 4.65-metre great white shark has been found dead in the nets at Sydney's Maroubra Beach, the NSW Government has confirmed.

The NSW Department of Primary Industries (DPI) said the dead shark was removed from the nets on Monday by contractors during a routine check.

Shark scientists have completed an autopsy.

Images of the shark in the net were shared on Facebook and Instagram.

Adam Cree, from Blue Reef Fishing Charters, saw the situation unfold and said it was the biggest shark he had seen.

"This morning I witnessed a boat checking the shark nets of Maroubra beach," he said.

"They looked like they were struggling to get something up.

"It was big. The biggest shark I've ever seen, and I've been running charters off Sydney for 20 years.

"We catch small sharks on a regular basis but not to that scale. That was definitely a man-eater, no question about it."

Adam Cree said spotting a shark of that size was unusual ( Supplied )

The beach, which is popular with surfers, was closed until about 11:00am, according to Surf Life Saving NSW.

Great white sharks measure about 120cm to 150cm at birth and can grow to at least six metres in length.

Mr Cree said while numbers increase at this time of year, spotting one is rare.

"We don't see too many sightings of shark that are that big," he said.

"They're more of a true oceanic or blue-water shark."