SYDNEY, Australia — A powerful earthquake measuring 7.9 hit the east coast of New Zealand’s South Island just before midnight there on Sunday, triggering multiple aftershocks and at least three tsunami waves, with seawater levels rising about six feet.
New Zealand’s civil defense and emergency management issued a warning for people living close to the coast to move inland, to higher ground.
The earthquake struck about 50 miles north of the town of Christchurch. Elliot Fim, a regional official, said in a telephone interview that there were no reports of damage, injuries or fatalities there. The fire department was dealing with a large number of emergency calls seeking assistance.
Mr. Fim said that people living along about 200 miles of coastline, from the small township of Kiakora and southward, had been evacuated. Some roadways and a building were reported damaged, but people had been able to move to high ground. A spokesman for the Wellington Region Emergency Management office said there were reports of minor damage in the city of Wellington.
Dan Jaksa, a duty officer from Geoscience Australia, said that if the small townships to the north of Christchurch did not have earthquake-resistant buildings, “it is going to be tough.”
Christchurch was struck in 2011 by an earthquake measuring 6.3 that devastated the town and killed 185 people. A further 164 people were seriously injured.
In Cheviot, a small town thought to be close to the epicenter, there were no reports of casualties. “There have been no deaths,” Grant Burnett, the chief of the Cheviot volunteer fire brigade, said in a telephone interview. “There is minimal damage to buildings that we can see. It is surprising, because it was a big quake,” he said.
Mr. Burnett said that some properties along the coast had been evacuated, but none were seriously damaged by the surge in seawater, which was over six feet in some places. The fire brigade had gone door to door to check on residents, especially the elderly, he said. “We are just a wee town. Everyone was O.K. We will be checking again in the daylight.”
Mr. Jaksa said the earthquake ruptured from west to east, with shocks moving toward the capital, Wellington, which is on the south coast of New Zealand’s North Island. “Let’s hope this is it, and there’s no more,” he said.
“Every time you go up one magnitude, say from 6.3 to 7.3, it is 32 times larger in terms of the energy released,” Mr. Jaksa said. This earthquake was about 40 to 50 times bigger than the one in Christchurch in 2011, he said.
After the initial 7.9 shock, there was an aftershock measuring 6.1, and then several more shocks, with three of those measuring in the high fives, he said. The earthquake occurred in the Hikurangi Trench, a subduction zone where one tectonic plate slides under another.
New Zealand’s North Island and the northern part of New Zealand’s South Island are on the Pacific plate, which is moving west, while the Australian plate is largely moving north. “This is the zone where the Pacific plate goes underneath the Australian plate,” Mr. Jaksa said, adding that the shift had caused a change in the seafloor that resulted in tsunami waves.