A heated exchange between an anti-vaccination campaigner and Northland GP Lance O'Sullivan has been caught on camera outside a Kaitaia venue where a controversial anti-immunisation documentary was screened last night.

Dr O'Sullivan, the 2014 New Zealander of the Year, and anti-vax campaigner Tricia Cheel, confronted each other before the screening of Vaxxed.

After exchanging strong views on vaccination outside, the video shows Dr O'Sullivan stride inside with Ms Cheel hard on his heels.

"You've made me turn into a nasty guy," Dr O'Sullivan says.

Ms Cheel hits back with: "No, you already are a nasty guy. I invited you in peace to watch this movie."

Dr O'Sullivan responds: "I was going to come anyway, dear."

To which an exasperated Ms Cheel says, "Well there you go."

The video was taken by a supporter of Dr O’Sullivan.

Inside, Dr O'Sullivan took to the stage, telling the audience their presence there "will cause babies to die", and saying he was there to continue his battle for his people "and importantly, for our children".

He said the idea of anti-immunisation has killed children around the world "and actually will continue to kill children whose parents are put off immunisation because of misinformation - misinformation based on lies".

Dr O'Sullivan has since been criticised on social media for his stance.

Laurence Bacchus, who works with the intellectually handicapped and high needs people at Hawke's Bay's Hohepa Services, wrote that Dr O'Sullivan is a "pharma whore" and a "disgrace to his profession", before adding "New Zealander of the year my arse!"

The film Vaxxed is a 2016 American film from anti-vaccination activists Del Bigtree and Andrew Wakefield.