A humpback whale trapped in waters south of Sydney has finally been freed after a gruelling eight-hour rescue mission.

Rescue efforts began on Saturday morning following reports of a whale in distress off Five Islands near Port Kembla.

Volunteer crews from Marine Rescue NSW and NSW National Parks and Wildlife Service were called to assist about 8.30am.

The whale, caught in a series of lines and floats, proved to be a challenge for rescuers to disentangle as weather conditions deteriorated and other whales in the area thwarted recovery attempts.

“A series of lines and floats were streaming from the whale,” Marine Rescue NSW inspector Glenn Sullivan told AAP.

A specialist National Parks Wildlife Service whale disentanglement team joined the operation just after noon.

Mr Sullivan initially said good weather conditions meant a successful rescue operation was likely.

But with a southerly wind change, fading light and other whales in the area it took rescuers more than eight hours to free the mammal which was untangled just after 4.30pm.

“The rescue crews are over the moon,” Mr Sullivan said.

“It’s now swimming on its own steam.”

Whale migration begins in May, when the mammals head north before starting their southbound journey in August.

The season peak occurs from June to July.