"We have aircraft in the air today conducting a 100 nautical mile radius search and boats in the water ready to respond," a spokesman for the department said.

"Safety is paramount and we ask the community to stay clear from the whale if they encounter it. This will keep you and the whale safe."

The whale was initially described as a juvenile humpback of about 4 metres. This was later updated by Portland's whale watching group to a "sub-adult" measuring 8-9 metres.

A 15-metre southern right whale was rescued near Portland less than two years ago after a four-day effort by DELWP officers to track it and cut it free from craypot ropes.

The whale, which has since returned to Portland waters, was dubbed "Tangles" by the hundreds of whale watchers who anxiously followed the rescue in August, 2018.

"Tangles" went missing for two days after first being spotted, but was detected in heavy seas after a search plane and boats were launched.

Large crowds lined cliffs around Portland to keep track of the whale. At a popular surfing spot known as Yellow Rock, several other southern right whales stayed close to the stricken animal as it struggled in the waves, as if guarding him.

Specialists eventually manoeuvred close enough to release the whale.

Four boats - a mother-ship, a support vessel and two smaller rigid inflatable boats - were used.

Once a rope with four large buoys was attached to the rope entangling the whale - a process known as kegging - rescuers used blades attached to long poles to cut away all the ropes.

It is understood trained officers within the depatrtment would be prepared to use a similar system to release the young humpback if it is found.

Portland has become one of the nation’s major whale-watching areas in recent years, with female southern right whales giving birth to calves in the sheltered bays and males arriving for mating, clearly visible from the district’s cliffs, beaches and breakwaters.

Winter is the peak season for whale watching in the area, though the world’s largest creatures, blue whales, can be seen during summer.