Department of Sustainability and Environment (DEPI) officers launched an air search on Tuesday morning along the coast between Port Fairy and Cape Otway and notified fisheries officers in South Australia.

A mother and calf were observed at Logans Beach Warrnambool, but none with entanglement.

"It can be very difficult to spot whales out to sea and it could also have travelled some distance by now," DEPI incident controller Mike Harper said.

"If we locate the whale, we'll then assess whether it's possible to reach it by water to attempt to disentangle it. "We have a number of trained and experienced staff ready to assist if it's found."

Warrnambool brothers Barry and Geoff Hose were about six kilometres off Warrnambool in a 16-foot boat when a passing whale, believed to be a southern right, snagged the anchor rope.

It towed them for about 60 metres at an estimated speed of more than 20 kilometres an hour before they cut the rope and headed home, relieved they weren't capsized.

Yesterday they featured in several radio station interviews as interest spread about their unusual close encounter with one of the ocean giants.

The home-made metal anchor had at least two metres of chain and 100 metres of rope attached when it was cut.

"This will be causing quite a bit of distress to the whale," Mr Harper said.

"An observation flight went up at 10am to search for the whale, concentrating on the waters between Cape Otway and Port Fairy."

Southern rights frequent the waters between Warrnambool and Portland in winter and early spring as they arrive to give birth and nurse their young. Humpback whales are also sometimes seen in the area passing through on their migratory path to Queensland.

The department said there were strict conditions and penalties to prevent swimmers and boats from getting too close to whales.

There is a 200-metre exclusion zone around all whales for boats and 300-metres for jet skis.

No vessels are allowed into the Logan's Beach whale nursery between June 1 and October 31.

DEPI said any sightings of entangled whales should be reported to the whale and dolphin emergency hotline on 1300 136 017.