An extensive search for a humpback whale that was tangled in rope off the NSW coast has been called off due to deteriorating conditions.
The mammal was spotted by a whale-watching boat on Tuesday 4km off Bondi Beach and while the crew was able to cut some of the ropes off, the animal wasn't entirely free.
A large-scale search was launched on Wednesday, including helicopter surveillance as far north as the NSW Central Coast.
NSW National Parks and Wildlife Service officers were assisted by volunteers from ORRCA, Marine Rescue NSW, commercial shipping, the boating community and the media.
However, there's been no sighting of the animal and NPWS spokesman Deon van Rensburg says despite the animal's size, the search has been "like trying to find a needle in a haystack".
"We have been forced to suspend the search until conditions improve," Mr Rensburg said, citing a Bureau of Meteorology gale warning for Sydney and Hunter waters.
The tough conditions made observations from the air, land and sea "virtually impossible", he said.
"There are a lot of whales heading north at the moment. Our crews saw plenty but none that were entangled."
Crews have been stood down but would be mobilised quickly should the animal be sighted, NPWS said.
The sub-adult humpback is believed to be somewhere in waters between Sydney and the Central Coast, and likely following a pod of whales heading north.
But if it was distressed, it might behave erratically and its location could have changed overnight, NPWS said earlier.
The annual migration of humpback whales involves about 30,000 animals making the trip north to breed and is one of the largest wildlife migrations on the planet.
The decision about whether to continue the search will be made on Thursday morning, taking into account the conditions.