A powerful earthquake that rocked New Zealand on Monday triggered landslides and a small tsunami, cracked apart roads and homes and left two people dead, but largely spared the country the devastation it saw five years ago when a deadly earthquake struck the same region.

Strong aftershocks continued to shake the country on Monday, rattling the nerves of exhausted residents, many of whom had spent a sleepless night huddled outside after fleeing for higher ground to avoid the tsunami waves.

The magnitude 7.8 earthquake struck the South Island just after midnight in a mostly rural area that's dotted with small towns. Near the epicentre, it opened up snaking fissures in roads and sparked landslides.

Hours later, a strong new earthquake with a magnitude of 6.2 rattled the country's South Island

A landslide blocks State Highway One and the main railway line north of Kaikoura on Monday following the earthquake. (Mark Mitchell/New Zealand Herald/Pool via AP)

New Zealand is planning to send in military helicopters and a navy ship to rescue about 1,000 tourists and hundreds of residents who remain stranded in the coastal town of Kaikoura.

Police said after the original quake that one person died in Kaikoura and another in Mt. Lyford, a nearby ski resort. There were also reports that several people had suffered minor injuries in Kaikoura, police spokeswoman Rachel Purdom said.

"From all directions, Kaikoura has essentially been isolated," Air Commodore Darryn Webb, the Acting Commander of New Zealand's Joint Forces, told The Associated Press. "There's a real imperative to support the town because it can't support itself."

Webb said the military planned to begin using four NH90 helicopters on Tuesday that could each transport about 18 people out of the town at a time. He said a ship was also leaving Auckland on Monday night that could potentially pick up hundreds of people if weather conditions allowed.

Chris and Viv Young look at damage caused by an earthquake along State Highway One near the town of Ward on New Zealand's South Island. (Anthony Phelps/Reuters)

"We're going to get as many people and belongings out as quickly as we can," Webb said.

He said the weather forecast wasn't looking great and the operation could take several days. He said that if needed, a C-130 military transport plane could drop fuel, water, food and other supplies to the town.

Prime Minister John Key flew over the destruction in Kaikoura by helicopter on Monday afternoon, as aftershocks kicked up dust from the landslides below. Cars could be seen lying on their sides and parts of the road were clearly impassable.

"It's just utter devastation. ... That's months of work," Key told acting Civil Defence Minister Gerry Brownlee as they hovered above the damage.

Key later toured the Kaikoura area and met with locals. He estimated the clean-up effort would run into the billions of dollars and said clearing the debris and blocked roads could take months.

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Kaikoura resident Terry Thompson, who added that electricity and most phones were also down in the town, a popular departure point for whale-watching expeditions.

Thompson was out of town but managed to reach his wife by cellphone during the night before her phone died.

"She said the glass exploded right out of the double ranch-slider," he said. "The neighbour's chimney was gone, there were breakages and things smashed everywhere."

His wife helped a 93-year-old neighbour and a tourist into her car and drove to higher ground, he said.

"They stayed in the car all night but couldn't sleep," Thompson said. "They're all very, very tired and concerned about the state of their property."

People wait in Wellington's Te Aro Park after nearby buildings were evacuated following an earthquake in New Zealand early Monday. (Hagen Hopkins/Getty Images)

New Zealand, with a population of 4.7 million, sits on the "Ring of Fire," an arc of seismic faults around the Pacific Ocean where earthquakes are common.

The earthquake caused damage in Wellington, the capital, more than 200 kilometres to the north and was also strongly felt in the city of Christchurch to the south.

Longer-lasting quake

Authorities in Wellington told people who work in the city's central business district to stay home on Monday. Officials said some large buildings were showing signs of structural stress, and the quake would likely have caused a mess in some buildings. The city's suburban rail network was shut while crews checked tracks, bridges and tunnels.

Hugh Sintes, of Christchurch, had just gotten into bed when the quake started and said he expected it to be over quickly.

He told CBC News Network the quake "intensified" and lasted about two minutes, not the 20 or 30 seconds he's used to after experiencing roughly a dozen earthquakes.

"The doors were swaying, the walls were moving, in the home that we're in. The light fittings, everything was moving. It was like the house had come alive," Sintes said. "We're on a concrete foundation and even the floor was alive."

A mannequin in a clothing store lies on a table after New Zealand's earthquake. Authorities urged people who work in the centre of Wellington to stay home on Monday. (Hagen Hopkins/Getty Images)

The quake was centred 93 kilometres northeast of Christchurch, according to the U.S. Geological Survey. The USGS initially estimated it had a magnitude of 7.4 before revising it to 7.8. It said the quake struck at a depth of 23 kilometres, after initially putting the depth at 10 kilometres. Earthquakes tend to be more strongly felt on the surface when they are shallow.

Regions able to cope with quake, PM says

Key said earlier officials had decided not to declare a national emergency because the nation's regions were able to adequately cope with the situation.

The quake temporarily knocked out New Zealand's emergency call number, 111, police reported.

The quake brought back memories of the magnitude-6.3 earthquake that struck Christchurch in 2011, destroying much of the downtown area and killing 185 people. That quake was one of New Zealand's worst disasters, causing an estimated $25 billion in damage.

The truck loading ramp at the Interisland Ferry wharf lays dropped and broken, in Wellington after the 7.8 magnitude earthquake struck. (Ross Setford/SNPA/Associated Press)

Although Monday's quake was stronger, its epicentre was deeper and much farther from major urban areas. Location, depth and other factors beyond magnitude all contribute to the destructive power of an earthquake.

New Zealand's Ministry of Civil Defence and Emergency Management reported that a tsunami wave struck at about 1:50 a.m. and warned residents living in low-lying areas anywhere along the country's east coast to move to higher ground.

There was confusion about the tsunami threat throughout the morning. The ministry initially said there was no threat but later wrote on Twitter "situation has changed - tsunami is possible" before reporting that a tsunami had hit.

When the quake hit, Christchurch resident Hannah Gin had just sat down in her living room to watch a replay of the national rugby team's weekend match against Italy when her house started shaking. Upstairs, her mother let out a scream.

The 24-year-old is accustomed to quakes in the temblor-prone region, so she said she sat calmly and waited, figuring the rumbling would stop in a few seconds. Instead, she said by telephone, the shaking went on and on — for at least three minutes, according to the clock on her phone.

"I could hear the sliding door sliding back and forth, and we've got washing hanging up and I could see the washing moving," Gin said. "It just kept going and going."