CHRISTCHURCH, New Zealand (Bloomberg)—A magnitude 7.0 earthquake struck New Zealand's South Island Friday morning, knocking out power, damaging buildings and rupturing pipes in Christchurch, the country's second-largest city, according to reports.

The quake, which was centered about 19 miles northwest of Christchurch, ruptured sewer lines and water pipes and closed the city's airport, Radio New Zealand reported. Tim Dower, a New Zealand journalist, told CNN that some building facades had collapsed. There were no initial reports of serious injuries.

The National Crisis Management Centre was activated to monitor the situation, said John Hamilton, director of Civil Defense & Emergency Management, in an e-mailed statement.

Aftershocks followed the initial 4:35 a.m. tremor, including one of magnitude 5.7 at 4:53 a.m., the U.S. Geological Survey said on its website.

The magnitude of the initial tremor was revised to 7.0 from 7.4 by the USGS. The Pacific Tsunami Warning Center said the quake didn't pose a tsunami threat.

Tremors were felt as far away as Greymouth, about 103 miles away, and in Dunedin, about 192 miles away, according to Radio New Zealand.

Power outages

Power was out in about half of Christchurch’s central business district and almost all of the city’s northern suburbs, the state public broadcaster said on its website.

Streets in the downtown part of Christchurch were blocked by police because of damaged buildings and debris, Radio New Zealand said. People were being asked to refrain from using their cellphones because of overloaded networks.

Damage was reported on the southern part of North Island, home to New Zealand’s capital of Wellington and Auckland, its largest city.

Christchurch is home to about 348,000 people, according to Statistics New Zealand. Mayor Bob Parker on Newstalk ZB Radio says the council is checking roads and sees sewer problems. Officials urged people to conserve water use.

New Zealand’s most powerful recorded earthquake hit in January 1855 with an estimated magnitude of about 8.2, according to GeoNet, an earthquake-monitoring site. It shifted vertically about 3,100 square miles of land.

Copyright 2010 Bloomberg