An earthquake with a magnitude of 7.8 struck central New Zealand just after midnight, the U.S. Geological Survey said, causing widespread damage and generating a tsunami.
New Zealand's Ministry of Civil Defence and Emergency Management warned of the risk of destructive waves along the country's entire east coast and urged residents in low-lying areas to evacuate and seek higher ground.
Waves of up to two meters (6 feet) could be possible for up to two hours, it said.
Anna Kaiser, a seismologist at GNS Science said a tidal signal or surge of up to one meter (3 feet) had been recorded in North Canterbury region of the South Island.
"That's reasonably significant so people should take this seriously," she told Radio New Zealand.
New Zealand's Geonet revised up its estimated magnitude of the quake to 7.5, from 6.6 earlier.
USGS said the quake was centered 91 km (57 miles) north-northeast of Christchurch, the biggest city on New Zealand's South Island.
A 6.3 quake there in February 2011 killed 185 people and caused widespread damage.
The tremor was felt throughout most of New Zealand. Some injuries had been reported but there no immediate reports of deaths.
"The whole house rolled like a serpent and some things smashed, the power went out," a woman, who gave her name as Elizabeth, told Radio New Zealand from her home in Takaka, near the top of the South Island.
Chris Hill, a fire officer in Cheviot, a coastal town near the quake's epicenter, said officials had gone door to door evacuating residents.
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