WELLINGTON, Nov. 14 (Xinhua) -- A severe earthquake rocked New Zealand's South Island early Monday, killing at least two people, damaging infrastructure and housing, leading to power outages and igniting a tsunami threat.
The magnitude-7.5 earthquake was centered 15 km northeast of Culverden, on the east of the South Island, and struck at 0:02 a.m. (1102 GMT) on Monday, according to the government's GeoNet monitoring service.
The quake was 15 km deep and was felt widely throughout New Zealand.
One fatality occurred at Mount Lyford, north of Christchurch, on the east of the South Island, and the other at a reported collapsed property in Kaikoura, on the northeast coast of the South Island, according to police.
Further casualties beyond the two confirmed deaths cannot be ruled out, said New Zealand's Prime Minister John Key.
Key and Acting Civil Defence Minister Gerry Brownlee said in a televised press conference that at least two fatalities had been reported, and emergency services were still trying to reach areas that had been cut off.
"On the very best information we have at the moment, we think it's only likely to be two, but of course there are isolated parts of the country in which we don't have perfect eyes on, so we can't be 100 percent sure, but we're not aware of any that we're not reporting," said Key.
"We don't have any indications at this point to believe that will rise, but we obviously can't rule that out because what's going to happen now as we have daylight is we can do a proper assessment," he said.
"Communities will obviously go out and reach out to their neighbors and their friends and their workmates to get a sense of the damage and making sure people get support," he added.
Air force and medical rescue helicopters were flying into the town of Kaikoura, which has been cut off by road and is believed to be the worst hit area, Key and Brownlee said. ( Structural engineers were also checking buildings in the capital, Wellington, where the quake was felt strongly.
Monday's quake was followed by hundreds of aftershocks, the largest of which had a magnitude of 6.3, 30 km north of Cheviot in the east coast of the South Island.
The Ministry of Civil Defence and Emergency Management (MCDEM) issued a tsunami threat message for most of the country's eastern coasts after the initial earthquake and urged residents living in low-lying areas to move to higher ground.
The first tsunami waves arrived at Kaikoura at around 1:50 a.m. (1250 GMT) on Monday, with waves of about two meters high, but it was too early to know what damage or casualties there might have been, said a statement from the MCDEM.
"Further waves should be expected and may be larger or more dangerous," it said.
The tsunami warning was later downgraded to a marine and beach threat, but the MCDEM still wrote on Twitter to urge people to stay off beaches, stay out of the water, and not to go sightseeing.
The MCDEM also urged people to conserve and boil drinking water for the next several days before household water supply is restored.
Key has called off talks in Argentina this week as his government deals with the aftermath of the deadly earthquake.
"I believe it is better that I remain in New Zealand in the coming days to offer my assistance and support until we have a better understanding of the event's full impact," he said.
New Zealand, with a population of around 4.7 million, is frequently rattled by earthquakes, most of which do no damage and cause no injuries.
Monday's quake, however, brought back memories of the 6.3-magnitude quake which killed 185 people in Christchurch in February 2011. That quake was one of the country's worst nightmares, causing an economic damage of around 25 billion U.S. dollars.