CHRISTCHURCH, New Zealand – A powerful 7.8-magnitude earthquake killed two people and caused massive infrastructure damage in New Zealand on Monday, but officials said they were optimistic the death toll would not rise.

The tremor, one of the most powerful ever recorded in the quake-prone South Pacific nation, hit just after midnight near the South Island coastal town of Kaikoura.

It triggered a tsunami alert that sent thousands of people fleeing for higher ground across large parts of the country’s rugged coastline before the threat abated.

Rescuers were left scrambling to reach Kaikoura, which had no telecommunications and was isolated by landslips, leaving officials fearing the worst.

But Civil Defence Minister Gerry Brownlee said 12 hours after the quake that a clearer picture of the damage was emerging.

"I think had there been serious injury or suspected further loss of life than we would have heard about it by now," he told Radio New Zealand.

He added: "It looks as though it’s the infrastructure that’s the biggest problem, although I don’t want to take away from the suffering... and terrible fright so many people have had."

Aerial footage outside Kaikoura – a popular departure point for international backpackers going whalewatching – showed railway tracks ripped up and tossed 10 metres by the force of the quake.

Landslips dumped hundreds of tonnes of rocky debris on the main highway while locals posted pictures of themselves near huge fissures that had opened up in roads.

One person was believed to have died at a historic homestead which collapsed at the town, while police were trying to reach the scene of a fatality at a remote property 150 kilometres north of Christchurch.

The earthquake struck at 12:02am Monday (1102 GMT Sunday) and was 23 kilometres deep, the US Geological Survey said, putting the epicentre in the South Island’s North Canterbury region.

It ignited painful memories for residents in nearby Christchurch, which was devastated five years ago by a 6.3 tremor which killed 185 people.

"It was massive and really long," Tamsin Edensor, a mother of two in Christchurch, said, describing the quake as the biggest since the 2011 tremor which was one of New Zealand’s deadliest disasters.

"We were asleep and woken to the house shaking, it kept going and going and felt like it was going to build up."

Soon after the earthquake, tsunami warning sirens were activated in South Island coastal towns and along the east coast of the North Island, with police and emergency workers going door to door to evacuate seaside properties.

The ministry of civil defence, responsible for emergency management in New Zealand, initially warned of a "destructive tsunami" with waves of up to five metres.

The first waves were measured around two metres and four hours later authorities downgraded the warning, but said risks remained.

Hundreds of aftershocks, some stronger than 6.0, continued to rattle the country in the hours after the main quake.

’Unbelievable damage’

In the capital Wellington, the city’s highest point, Mount Victoria, was choked with cars as residents from low-lying areas sought refuge from a possible tsunami.

Shattered glass littered inner city streets, with rail and bus services cancelled as officials told people not to commute to work.

Prime Minister John Key said his office in the parliament building known as The Beehive was trashed, although there was no structural damage.

"The damage is unbelievable. It must have been really moving, there’s just broken glass, pottery, televisions, computers - everything’s gone south in a major way," he said.

Earthquake engineer Ken Elwood from the University of Auckland said the impact would have been much worse had it hit at lunchtime, like the Christchurch one.

"When it happens in the middle of the day it’s a very different story," he told TVNZ.

"People were safe in their homes, homes might get damaged but they’re safer for the people inside and that’s certainly the blessing of this earthquake."

In several cities guests were forced to evacuate hotels when the quake hit, including Nelson, about 200 kilometres from the quake centre where the touring Pakistan cricket team were given a scare.

"Some of the boys were in prayer, some were watching the India-England Test on TV when we felt the windows shake," team manager Wasim Bari told ESPNcricinfo.

New Zealand is on the boundary of the Australian and Pacific tectonic plates, which form part of the so-called "Ring of Fire", and experiences up to 15,000 tremors a year. – AFP