A major earthquake whose, initial reported magnitude of M7.5 was initially lowered to M6.6, only to rise up to M7.8 in the latest USGS estimate, struck central New Zealand northeast of Christchurch just after midnight, or 12:02am local time on Monday, (1102 GMT Sunday), the U.S. Geological Survey said, generating a tsunami that hit the northeast coast of the South Island.
The quake - which had a shallow depth of just 10km like the recent destructive earthquakes to strike Italy - was centered centered 46km from the town of Amberley with about 2,000 people, and 70km from the town of Kaiapoi with 10,000 residents, according to the USGS. It was felt throughout most of the country.
The quake took place 91km from the town of Christchurch which was struck by a powerful earthquake back in 2011. At least 185 people were killed and hundreds injured after the 6.3 magnitude quake hit the town. The quake shook the captial city Wellington, where sirens were heard.
There were no immediate reports of any major damage or injuries in Christchurch.
The New Zealand Ministry of Civil Defence and Emergency Management (MCDEM) issued a tsunami warning for the eastern coasts of North and South Islands, warning residents along the country's entire east coast to seek higher ground.
This is a local source event - we don't have info about specific locations. The tsunami threat is for the East Coast of all NZ #eqnz— MCDEM (@NZcivildefence) November 13, 2016
Shortly after that, Burwood Ward Councillor Glenn Livingstone wrote on Twitter that a “2m high tsunami” hit the town of Kaikoura and moved away from the coast. MCDEM warns the first wave may not be the largest, as tsunami activity is expected to continue for several hours.
Anna Kaiser, a seismologist at GNS Science said a tidal signal or surge of up to one metre (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.
The tremor, which was measured by New Zealand's Geonet at magnitude 6.6, was felt throughout most of New Zealand. Civil Defence said it was too early to assess the damage or whether there had been any injuries or 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.
Residents in Wellington said glass had fallen from buildings into the streets.
Yowzer! Now they say 6.5 Hanmer not 7.5 Cheviot pic.twitter.com/7smm8fLSgd— Alyson Baker (@Shiretane) November 13, 2016
The main tremor was followed by a series of strong aftershocks and there were reports of damaged buildings in the small rural township of Cheviot near the epicentre.
"It was massive and really long," Tamsin Edensor, a mother of two in Christchurch, told AFP, describing the powerful quake as the biggest since the deadly 2011 tremor.
"We were asleep and woken to the house shaking, it kept going and going and felt like it was going to build up."
In a brief message the 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. However, the national civil defence organisation, which is in charge of New Zealand's emergency management said a tsunami was possible.
"The first wave activity may not be the most significant," it said in a bulletin, adding tsunami activity would continue for several hours.
Anna Kaiser, a seismologist with the GNS Science, said the government's earthquake monitoring service, the quakes were close to the coast.
"They've been quite large. We've also seen a signal on the tide gauge at Kaikoura which is up to one metre (three feet) so it's reasonably significant, so people should take this seriously."
In September, a strong 7.1-magnitude earthquake struck the east coast of New Zealand, generating a small tsunami, but no significant damage or injuries were reported.
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.