The last thing police expected when alerted to a suspicious hole outside a Christchurch hospital was to crawl down a crudely dug tunnel to find a man at the other end primed to burn a "death machine" to the ground.

At least four times - on Labour Day, Guy Fawkes day, New Year's Eve and the night he was arrested - Graeme Richard White crawled through his tunnel to deposit firelighters, matches, candles and kerosene-soaked string underneath an abortion clinic at the Lyndhurst hospital.

The fanatical Christian anti-abortionist had also begun to disable the clinic's sprinkler and alarm system.

The judge who sentenced White, aged 39, to 2 1/2 years in prison this week described his behaviour as a "sinister development in New Zealand which had until today escaped the extremes of anti-abortion protest elsewhere."

White spent most of his days protesting outside the gates of Lyndhurst Hospital.

But what clinic staff did not realise was that by night he was tunnelling under the perimeter fence towards the hospital, where he eventually broke through into a space under the floorboards.

He was caught early on April 28 when a security guard noticed the tunnel entrance outside the hospital fence.

Police crept through the tunnel to find White squatting under the floorboards wearing a black balaclava and with a crowbar.

White had told friends of his plans to burn the clinic down two months before he began tunnelling.

But White told the jury, which convicted him of four counts of burglary and possessing tools for burglary, that he did not intend to torch the clinic.

He said he did not want to hurt anyone - his goal was to stop crimes against the human race and to get the chance to raise his concerns in court.

"Part of the reason I went to the hospital was I believed the people in the building were in grave danger. Not just the unborn children and the women going there but also the people who were running the place," White told the court.

He believed abortion was violence and that "violence can only give birth to more violence."

But Judge Doherty said White had the potential to cause considerable harm. "You claim to be a pacifist but there is a certain incongruity to that claim," he said.

"You seem prepared to commit wanton acts under the guise of non-violent protest."

New Zealand has a relatively peaceful history in anti-abortion protests, unlike the US where violence is common. In 1998, a New York abortionist was gunned down outside his home by a pro-life campaigner.

There have also been arson attacks, bombings and use of poisons on abortion clinic staff.

There is no evidence that White's actions in April last year signal a trend in violent anti-abortion protest in New Zealand.