Sydney, Aug 23 : Rescue crews have resumed efforts to free a juvenile humpback whale entangled in Sydney Harbour fishing nets.

As of Friday morning, police and maritime authorities were tracking the whale and enforcing an exclusion zone near Bradleys Head -- a peninsula protruding from the harbour's north shore -- as it dragged a line with buoys attached, Xinhua news agency reported.

A whale-watching group spotted the whale in distress on Thursday noon, but initial attempts to detach the netting wrapped around it were suspended due to the failing light.

Rescuers led by volunteers from the wildlife group, the Organisation for the Rescue and Research of Cetaceans in Australia (ORRCA), attached a GPS tracker to the whale on Thursday.

"Hopefully the conditions are favourable, the tracker works and the whale is freed nice and early in the morning," ORRCA President Ashley Ryan told Nine Entertainment newspapers on Thursday night.

However, the tracker became dislodged shortly afterwards. The whale was again spotted by authorities at 7:30 a.m. local time on Friday after initial fears it had swum out of the harbour overnight.

ORRCA on Wednesday asked for residents of New South Wales to help track three separate humpback whales spotted entangled in nets off the eastern state's coast between the cities of Newcastle and Tweed Heads north of Sydney.

"The behaviour of entangled whales can be unpredictable, and they can change directions of travel," it said in a statement on social media.

For decades, humpback whale populations were hunted to the brink of extinction -- at one stage there were only an estimated 1,500 of the animals left in Australian waters.

But they are a rare conservation success story after global protections were afforded to the whales in 1965.

Humpback whale numbers now exceed 40,000 -- a number close to pre-whaling levels -- and the marine animal has since been removed from Australia's threatened species list.

/IANS