The rats were targeted by poison dumped from helicopters

Rats arrived on Campbell Island 200 years ago from sealing and whaling boats.

They multiplied throughout the 11,300-hectare (27,900-acre) island and wreaked havoc on the native seabird population.

But now, two years after tons of poison pellets were dumped from the air, Campbell Island has been declared rat-free.

"After 200 years of rat occupation, Campbell is now a safe haven for the millions of seabirds that breed there," New Zealand Environment Minister Chris Carter said in a statement.

"This is a fantastic result... It is a proud day for New Zealand conservation and proves once again that we are the world leaders in pest control and protection of our native species."

Unique species

The manager of the eradication project, Andy Roberts, said the island used to have the largest population density of rats anywhere in the world.

About 200,000 rodent inhabitants were exterminated in the government's 2.6m New Zealand dollar ($1.5m) scheme on the island, which now has no human residents.

The incomers had reduced the island's shearwater seabird population to a handful, "which will take hundreds of years to recover," he said.

Unique species including the flightless Campbell Island teal and the tiny Campbell Island snipe had only survived eradication because they were removed from the island by environmentalists.

They can now be reintroduced to the island, which lies 700 kilometres (440 miles) south of New Zealand.