Cane toads are spreading across Australia at a rate of 50 kilometres a year, which has scientists worried about their potential to wreak havoc with that country's ecosystem.

The poisonous toads, which can weigh up to two kilograms, were introduced to northern Queensland in 1935 to control beetles that were destroying sugar cane crops.

However, they have become a much bigger pest themselves.

Cane toads with relatively longer legs move faster over a short distance. (Courtesy: Ben Phillips)

They have expanded their habitat to more than one million square kilometres in eastern and northern Australia, eating or poisoning native fauna and threatening crops.

Australian researchers who studied the toads suggest pest-control measures should be launched "as soon as possible, before the invader has time to evolve into a more dangerous adversary."

Radio tracking of the toads "confirmed the astonishing locomotor performance in these animals, which move up to 1.8 kilometres per night during the rainy months," the biologists report in Thursday's issue of the journal Nature.

The distance sets a record for any frog or toad, the researchers said.