CHRISTCHURCH • A powerful magnitude 7.8 earthquake has rocked New Zealand, damaging buildings and triggering a tsunami which saw people in coastal areas fleeing to higher ground.

The Ministry of Civil Defence, responsible for emergency management in New Zealand, called the tsunami "an event of life-threatening or national significance".

However, the Pacific Tsunami Warning Centre said that based on available data, "a destructive Pacific-wide tsunami is not expected".

The shallow quake was centred some 90km north of the South Island city of Christchurch and felt throughout the country.

Although no injuries were reported, there were reports of widespread damage, with electricity and phone services cut off in many areas.

The quake struck at 12.02am Monday local time (7.02pm Sunday Singapore time) and was 23km deep, the United States Geological Survey reported. It ignited painful memories for residents in Christchurch, which was devastated five years ago by a 6.3 magnitude quake that killed 185 people in one of New Zealand's deadliest disasters.

Ms Tamsin Edensor, a mother of two in Christchurch, said the latest quake was "massive".

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

A woman who gave her name only as Elizabeth told Radio New Zealand (RNZ) from her home in Takaka, near the top of the South Island: "The whole house rolled like a serpent and some things smashed, the power went out."

The main quake was followed by a series of strong aftershocks. There were reports of damaged buildings in the small rural township of Cheviot, near the epicentre.

In a short message, New Zealand Prime Minister John Key tweeted: "I hope everyone is safe after the earthquake tonight."

The ambulance service said it did not receive any reports of quake-related injuries but people took to social media to report damage, such as goods tipped from shelves and shattered glass littering streets.

"Family friends in Cheviot say some houses are gone," one person tweeted.

Mr Richard Maclean, a spokesman for the Wellington City Council, said residents had been evacuating the city's southern coastal suburbs because of the tsunami threat and there had been reports of structural damage to several buildings. "We've got reports of broken water pipes and lots and lots of things off desks and shelves," he told RNZ.

The Civil Defence Ministry, which urged people in the eastern coastal areas to move to higher ground, said "a destructive tsunami is possible". "The first wave may not be the largest. Waves may continue for several hours," it added.

Mr Simon Morton, a radio presenter in capital city Wellington, said he had evacuated his house after noticing the tide dropping away. Other people had joined him in going to higher ground.

Seismologist Anna Kaiser of GNS Science, the government's earthquake monitoring service, said the quakes were close to the coast and there had been tidal movement up to 1m in the South Island town of Kaikoura. "It's reasonably significant, so people should take this seriously," she said.

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.

Meanwhile, a 6.2 magnitude earthquake hit north-western Argentina yesterday, the US Geological Survey said, but there were no immediate reports of damage. The quake struck shortly after 8am local time, north of the city Chilecito in the nation's La Rioja province.

AGENCE FRANCE-PRESSE, REUTERS