[Seth Jaworski]

Australian Associated Press

Two dangerous and exceptionally grumpy Australian crocodiles have escaped their restraints and caused havoc on a flight to New Zealand.

Saltwater crocodiles Scar, from Darwin, and Goldie, from Cairns, are the first of their species to be flown across the Tasman - and the pair weren't going to take the relocation lying down.

The duo broke their head restraints mid-flight, thrashing so hard that the Hercules plane transporting them shuddered and shook.

"It got pretty exciting on board, that's for sure," said John Dowsett, general manager of Auckland's Butterfly Creek Zoo, which the crocs now call home.

"The plane was shaking and the pilot turned to me and said `that's your crocs having a bit of a go'.

"We gave them drugs, a muscle relaxant to calm them down, and that seemed to work but boy, are they powerful.

"You can see why we needed the Royal New Zealand Air Force on this job."

The Hercules was the only aircraft deemed large and sturdy enough to transport the monster predators.

Both male, they are four metres long and weigh over half a tonne each, and are now the largest, and most dangerous carnivorous predators in New Zealand.

The pair might have been groggy and "a bit grumpy" on arrival in Auckland midnight on Tuesday but they have since settled into the zoo where they are soon to become the star attractions.

They form the centrepiece of a new saltwater crocodile exhibit, sponsored by Tourism NT, that will also feature several baby American alligators.

Mr Dowsett said they will live in a 32 degree billabong - "a heated Sheraton" - but they won't be cosying up together.

Their New Zealand keepers have been told to keep the pair apart in separate exhibits so they don't kill each other.

"They're extremely aggressive so you don't want them anywhere near each other," he said.

"When you see them in the wild they've always got shreds torn off them. We don't want to see that here too."

Despite their apparently bad tempers, Scar and Goldie are believed to have relatively stable personalities and not the "absolute craziness" displayed by some of their kind, the zoo manager said.