A pod of killer whales, also known as orcas, has been sighted near Bruny Island and the Iron Pot at the mouth of the River Derwent.

The sighting of what appears to be a large male orca and several smaller whales was reported to the DPIPWE Marine Conservation Program this afternoon.

Marine biologist Rachael Alderman said there had been only a handful of sightings of the species close to Hobart in the past 10 years.

"It doesn't happen very often, it is a pretty special sight," she said.

"But we know there are fairly regular sightings of killer whales up and down the coast of Tasmania, particularly ... the east coast."

Dr Alderman said the species was known for travelling long distances in a short amount of time and it was possible the whales could have journeyed from the coast of New South Wales.

"I had a call on the hotline just a few days ago, up the east coast, so this may well be that same pod travelling down," she said.

Dr Alderman said although orcas had travelled up the Derwent River as far as Sandy Bay in the past, the pod seen on Monday afternoon may have already travelled south and back out to sea.

"Part of why we're really interested in hearing about them, getting as much information as we can and images, is so we can learn more about their behaviour," she said.

"Who we're dealing with, where do they live, how are they foraging, and just understand a bit more about the ecology of these species and how important Tasmania is for them."

Whale sightings in Tasmania can be reported to the DPIPWE Whale Hotline: 0427-WHALES (0427 942 537).