Sydney  - Animal lovers Thursday rigged up a feeding device they say could keep a month-old humpback alive long enough for its mother to reclaim it from a sheltered Sydney bay where it has been trying to suck milk from the hulls of yachts.

But animal welfare officers have told them to leave the calf alone and let experts decide its fate.

The 5-metre calf somehow got separated from its mother last week and is growing weaker by the day.

Marine biologists say keeping the pathetic creature alive is impossible and have urged distraught animal lovers to accept that it should be put out of its misery.

"To hold it here and feed it ... and then somehow get it to Antarctica where it would learn to feed on krill is simply impossible," whale expert Nick Gales said. "And I think it is often the kindest, the most humane, thing to do is to euthanize the animal and prevent it just suffering a very long protracted starvation and death."

The 2-ton whale stayed alongside when a yacht it had been nuzzling was towed out to sea in the hope that either its mother or another lactating female would respond to its calls. But a day later the whale that the media has named Colin after the yachtsman who found it, was back in the bay.

An outpouring of sympathy for the whale has prompted politicians to call in international experts, and even the armed forces, to give it a chance of life.

"Our hearts are breaking with what's happening with baby Colin," New South Wales state premier Morris Iemma told reporters. "It's looking bleak, but every effort is being made." (dpa)