A WHALE calf that seems to think a yacht is its mother is likely to die in days if it does not find another mother to adopt it, wildlife officials say.

The humpback calf, aged four to eight weeks, was first sighted on Sunday in waters off Sydney, and on Monday tried to suckle from a yacht, which it would not leave. Rescuers towed the yacht out to sea and the calf finally detached from the boat, but the creature returned to an inlet near Sydney yesterday.

The lost calf cannot survive without milk for long, said John Dengate of New South Wales National Parks and Wildlife Service.

"It's probably a question of days rather than weeks," he said.

Artificial feeding would be impossible, so the calf's only chance is to find another female whale which was lactating because she had a calf of her own, he said.