The crocodiles will be hungry and very dangerous after their long trip, according to Mick Pittman of the Cape York Consultancy Group.

His warning was broadcast on Radio Australia on Friday.

Mr Pittman said the saltwater crocodiles are in search of new breeding grounds because many rivers in Papua New Guinea have dried up.

Saltwater crocodiles are fiercely territorial

Some had already reached Cape York, Australia's northern tip, he said, adding that they will roam the coastline staking new territory.

Saltwater crocodiles are found primarily in the brackish water of tidal rivers. However adults may venture out to sea and swim between islands.

Dr Adam Britton, author of the Crocodilian website, says individuals have been known to travel over 1000km (625 miles) by sea.

Most saltwater crocodiles eat fish, amphibians, reptiles, birds and small mammals, he says.

Very large animals will eat almost anything, including wallabies, other crocodiles, cattle or even people.

In Australia, however, there have been only 14 fatalities in the last 27 years, Dr Britton says.

In most cases the victim was swimming.

Saltwater crocodiles may live for up to 70 years or more, and reach a length of five to six metres.