A "weird puking bird" with a bizarre mating dance has won New Zealand's annual avian beauty contest, triumphing after British comedian John Oliver launched an unlikely global campaign.

The unfancied Australasian crested grebe soared to an unexpected victory in the Bird of the Century ballot on Wednesday, backed by voters from far-flung cities including Tokyo, London and Paris.

Oliver used his popular television show to meddle in New Zealand's beloved competition, urging viewers to back the species more commonly known by its Maori name "puteketeke".

Baffled organisers were soon in a flap as tens of thousands of votes poured in from countries across the globe, briefly crashing counting systems.

With a striking plumage of black, white and brown, New Zealand's online bird encyclopaedia celebrates the water-loving puteketeke as a "majestic and distinctive" species.

Oliver, meanwhile, less charitably dubbed it the "weird puking bird".

Puteketeke are known for eating their own feathers in an effort to trigger their gag reflex and throw up parasites, said competition organiser Nicola Toki from conservation group Forest and Bird.

"Puteketeke began as an outside contender, but was catapulted to the top spot thanks to its unique looks, adorable parenting style -- and propensity for puking," Toki said.

They are also known for a strange and elaborate mating ritual which they perform with gusto but apparently limited success -- it is believed New Zealand's puteketeke population has dwindled below 1,000.

It involves enticing a potential mate with weeds dangling from their beaks, before chest bumping them and engaging in a chorus of chirps that experts have called the "growling cat display".

"I have never identified with anything more," Oliver said.

'Alarmingly aggressive campaign'

Oliver, the star of US television show Last Week Tonight, hijacked the vote with his self-styled "alarmingly aggressive campaign" after discovering the competition was not restricted to New Zealanders.

He said he erected billboards imploring the people of Mumbai, Tokyo, Paris and London to have their say.

Organisers said they ended up tallying over 350,000 votes sent from almost every nation on the planet -- smashing the previous record of 56,000.

But Oliver's meddling and so-called "fowl play" has also upset many in the bird-proud nation, with organisers forced to discard tens of thousands of suspect votes -- including 40,000 cast by a single person for a penguin.

"We know birds inspire incredible passion, but we encourage people to channel that passion into productive efforts rather than trying to rig an election," Toki said.

Birdwatcher Michael Burton-Smith told local media the overseas votes "ruffled the integrity" of the campaign.

The good-natured competition is never short of controversy, with past polls plagued by suspicious numbers of Russian votes, and accusations that neighbouring Australians were trying to rig the competition.

The kakapo, a chubby flightless parrot resembling a green-feathered bowling ball, was disqualified from last year's competition because it had already won too many times.