GOLD COAST (AFP) - Australian authorities struggled to rescue a beached baby whale Wednesday and were forced to suspend the operation as fading light hampered efforts to return it to sea.

The whale, reportedly a two-year-old humpback, washed up on Palm Beach on the popular Gold Coast late Tuesday, with rescuers working for hours to try and free it.

Hundreds of people gathered at the Queensland beach to watch the rescue, which included fitting a specially-designed harness to the mammal as workers from marine park Sea World tried to coax it back into the water.

Rescuers were able to briefly return the whale to sea before it became stuck on a sandbar slightly further offshore.

Sea World's director of marine services Trevor Long told the Australian Broadcasting Corporation the whale "looks in good condition" and "seems robust enough" despite its situation.

"It is doing all the right things. It is breathing quite good, it is making all the right vocalisations but we don't know what's happening inside," Long said.

The rescue attempt was suspended in fading light when it became too dangerous to be in the water with the whale, ABC reported.

Sea World's marine animal supervisor Tacha Mulligan said she and her colleagues were trying to keep the whale cool, wet and comfortable.

"We're looking at a 15- to 20-tonne animal that's up on the beach so we'll be doing our very best to make sure it's as stress-free as possible," she told the Brisbane Times.

She added that it was not known why the whale beached itself.

"It simply may have lost its way, it may have an underlying medical condition that we're unaware of right now until we get those medical samples (we took from it) back." Whale beachings are relatively common in Australia, but scientists do not know why they happen.

Humpback whales are currently on their annual southern migration from Antarctica to warmer waters in Queensland state to give birth and mate.