Two large aftershocks - including one measuring 6.3 - have struck towns already cut off by a magnitude 7.5 earthquake that's claimed two lives, caused major landslips and destroyed highways in New Zealand's South Island.
A severe magnitude 5.7 quake struck 20 kilometres east of Seddon at 1.34pm (local time) on Monday, shaking Wellington, and several smaller South Island towns that felt the worst of the main tremor
That earthquake was almost instantly followed by a magnitude 6.3, 30 kilometres north of Cheviot.
The area has been subject to a steady stream of aftershocks since the 7.5 magnitude quake centred near Hamner Springs just after midnight.
Prime Minister John Key said two people were confirmed fatalities after the quake but it was not yet clear if both were as a direct result of the tremor.
Police earlier said a casualty was reported at the heritage-listed Elms Homestead at Kaikoura and another person was believed dead at a house at Mt Lyford, north of Christchurch.
A tsunami warning which had been in place remains in effect but has been downgraded.
Mr Key said a Defence Force helicopter was heading to Kaikoura after access to the coastal town was cut off by slips and ruptured roads and he would fly to the town on Monday afternoon to inspect the damage.
An Air Force Orion had surveyed main transport routes between Picton and Christchurch.
Schools and early childhood centres from Wellington to Canterbury would remain closed until they have been assessed.
In the aftermath of the quake the Ministry of Civil Defence and Emergency Management warned a destructive tsunami was possible and urged those in eastern parts of the country in low lying areas or near the coast to move.
The ministry revised down the tsunami risk but said the area from Wellington to Banks Peninsula could still get waves of up to 1m while people were urged to stay away from beaches and waterways in other parts of the country.
Four homes in Christchurch abandoned by owners after the tsunami warning had been burgled, police said.
A state of local emergency was declared by Hurunui District Mayor Winton Dalley just before midday. Hanmer Springs and Cheviot are within its boundaries.
The initial quake was registered as a 6.6 shake before being upgraded by GeoNet seismologists.
Australian PM offers support to NZ
Prime Minister Malcolm Turnbull has phoned his New Zealand counterpart to offer support after the deadly overnight earthquake.
Mr Turnbull says even John Key's office in Wellington was shaken by the 7.5 magnitude quake, which has claimed two lives.
He told media on Monday that he had conveyed to Mr Key Australia's "absolute solidarity" and that Australia wiould make "all resources available" to the country.
"I passed on to John our sincere condosalences on those deaths. I hope ther ewill ne no others identified
Tsunami warning
A seven-person Fire Service urban search and rescue team was flown by helicopter to Kaikoura and two further assessment teams have been deployed, one to Waiau and one to Blenheim.
Some areas remained without power after the quake and phone services, both mobile and fixed line, were affected in the Kaikoura area.
The national crisis management centre had been activated but a national state of emergency had not been declared.
People in Cheviot, near the epicentre of the first quake, reported extensive damage.
"Family friends in Cheviot say some houses are gone" a woman named Brodie tweeted.
In Wellington some buildings were damaged and windows were smashed.
Wellington Region emergency controller Bruce Pepperell said a number of major buildings were showing signs of "structural stress" an inner-city workers were told to stay at home.
Inspections were being carried out on bridges and tunnels around the region he said many buildings would need to be checked for damage.
KiwiRail said it had suspended trains on the main trunk line south of Palmerston North in the North Island and north of Christchurch in the South Island. A train was stranded north of Kaikoura after the quake.
Cook Strait ferry sailings have been cancelled and about 20 passengers aboard the Kaiarahi spent about 12 hours longer than planned on the vessel after it was unable to dock at Picton.
State Highways in the South Island have also been closed - SH1 Picton to Waipara and SH7 Waipara to Springs Junction, and many other local roads had also been damaged.
The quake comes almost six years after a destructive 6.3 earthquake that killed 185 people in Canterbury early in 2011.
Source: AAP
