New Zealand Earthquake: Two die after massive tremors

There have been two fatalities after a series of huge earthquakes overnight, Prime Minister John Key says.

Authorities were scrambling this morning to assess damage and respond to reports of injuries after the first, 7.5 magnitude earthquake centred near Hanmer Springs.

The Ministry of Civil Defence and Emergency Management confirmed there had been two deaths from the earthquake.

One person died in a house that collapsed in Kaikoura, and a second person died at a house in Mt Lyford, north of Christchurch.

Mr Key said a Defence Force helicopter would be flying to Kaikoura and another one would be available in Wellington.

An Urban Search and Rescue team from Christchurch was also on its way to Kaikoura by helicopter, along with two further assessment teams deployed to Waiau and Blenheim.

As a result of the quake, Mr Key cancelled his proposed trade trip to Argentina, and will decide later this week whether to attend APEC in Peru next weekend.

Nelson Marlborough District Health Board said five people had been admitted to Wairau Hospital by early this morning with various injuries, some described as moderate.

The first quake struck at 12.02am, near Hanmer Springs, at a depth of 15km. It was followed by a series of large earthquakes across New Zealand up to 6.2 in magnitude, which prompted tsunami alerts, causing residents of coastal areas to flee inland.

GNS science said there had been about 250 aftershocks since the massive shake just after midnight, with 33 of them above magnitude 5, and three of magnitude 6 and above.

Most were in the upper South Island, in Seddon and Kaikoura, but a 4.9 magnitude earthquake hit Paraparaumu and a 4.9 hit Wellington in the early hours.

The Civil Defence ministry said roads were closed on State Highway 1 between Blenheim and Picton, State Highway 6 between between Blenheim and Nelson, and State Highway 7 between Springs Junction and Waipara.

It warned people to check for any dangers on damaged properties including to gas and water supplies.

The earthquake sequence is the biggest since the 5.7 Valentine's Day earthquake, which caused cliffs in the Christchurch suburb of Sumner to fall and liquefaction in some east Christchurch areas.

Tsunami activity was detected in Kaikoura and Wellington, with initial tsunami warnings prompting sirens from Northland to Christchurch, and waves detected in Wellington and the South Island.

A tsunami at least 2m high was recorded near in Kaikoura, Civil Defence tweeted.

The Chatham Islands and the region between Blenheim and Banks Peninsula were still prone to a marine and land threat, the Civil Defence ministry warned.

KiwiRail said all trains on the North Island Main Trunk line, south of Palmerston North, and in the South Island had been cancelled until further notice.

Ferry sailings were also cancelled until a full assessment could be made of the terminals in Wellington and Picton.

The Ministry of Education advised schools and early childhood centres from North Canterbury through to Wellington would remain closed today.

It also said all NCEA scholarship exams would be suspended.