New Zealand: 7.8-magnitude quake rocks south, triggers tsunami
New Zealand is a South Pacific nation of islands, the two largest being the North and South islands, which are home to most of the population.
(CNN) -- A powerful 7.8-magnitude earthquake has rocked New Zealand's South Island, triggering a tsunami as people fled buildings in a panic and were told to seek higher ground.
The quake struck around 50 kilometers (around 30 miles) northeast of the city of Christchurch just after midnight local time on Monday, the US Geological Survey reported. Waves of 2.49 meters above usual tide levels were measured near the epicenter by the Pacific Tsunami Warning Center (PTWC).
The country's entire east coast is at threat of dangerous waves, the New Zealand Civil Defense said on Twitter in an advisory, adding that initial waves may not be the largest and that they could continue for several hours.
"Move inland or to higher ground immediately," the warning said.
New Zealand is a South Pacific nation of islands, the two largest being the North and South islands, which are home to most of the population. Slightly more than 1 million people live in the South, while the North has more than 3 million.
In Christchurch, memories of a devastating 6.3-magnitude earthquake in 2011 are still fresh for many. That quake killed 185 people and injured thousands, and reduced swathes of the city's historic area to rubble.
"The land has been very peaceful for many, many months. So this is bringing back all the rare memories," Chet Wah, owner of Designer Cottage B&B in Christchurch, told CNN.
"I just checked with all the guests. They are alright. It is scary. It's going to be a long night."
Christchurch, on the South Island's eastern coast, has a population of over 340,000 people, the most recent census shows.
Images emerged on social media of grocery items fallen off supermarket shelves and water rocking back and forth in swimming pools.
And at least three aftershocks hit near South Island, the USGS said, some with a magnitude as high as 6.2.
"This is the strongest [earthquake] I've ever felt," Tamara Hunt told CNN. She was with her husband at their home in Whanganui when the earthquake struck.
"It started off so small, like the cat moving in the bed, but then it started building and I had to run to the door. Stuff in the house was falling over and the doors were swaying really bad," she said. "Then we decided to get out, and that's when we saw our pool had lost a lot of water. The earthquake went on for two minutes."
The USGS initially reported the quake's magnitude at 7.4 at a depth of just 10 kilometers -- shallow enough to cause serious destruction to the immediate surrounding area. It later revised the quake strength to 7.8, but changed its depth to 23 (14.2 miles) kilometers, giving more of a buffer between the epicenter and the Earth's surface.
New Zealand is regularly hit by earthquakes as it sits in a "collision zone" between the Indo-Australian and Pacific tectonic plates. It is part of the Pacific's "Ring of Fire," a horseshoe-shaped belt around the ocean's edges where many earthquakes and volcano eruptions occur.
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