A humpback whale entangled in rope has been freed by rescuers during a dramatic operation in Sydney Harbour.

The humpback whale, part of a pod of whales travelling through the harbour, was spotted north of Sydney Harbour on Tuesday afternoon dragging a buoy behind it.

It was later confirmed that the whale was entangled in 100m of rope and a number of buoys.

National Parks and Marine Rescue were called after a fisherman spotted the animal near Bundeena in Sydney's south.

As of 2:00pm, the whale was just north of Sydney Heads. Authorities managed to free the whale about 2.20pm after working on the rescue for about an hour.

They attached a number of large buoys to the rope that had entangled the humpback in order to slow it down and worked to untangle it.