According to the U.S. Geological Survey, the earthquake occurred at 4:35 a.m. local time Saturday, and lasted for approximately 40 seconds. The epicenter of the quake was 19 miles northwest of the city of Christchurch, New Zealand's second largest urban area with approximately 375,000 residents.
The quake was also felt in New Zealand's capital, Wellington, 186 miles from the epicenter.
Widespread damage and power outages have been reported, according to The Press, a Christchurch paper. Radio New Zealand also reported that some roads had been rendered impassable, and that several of the city's bridges had been damaged.
"Just unbelievable," Christchurch resident Kevin O'Hanlon told The Press. "I was awake to go to work and then just heard the massive noise and, boom, it was like the house got hit. It just started shaking. I've never felt anything like it."
Area hospitals are treating scores of residents for minor injuries, though no fatalities have been recorded so far, MSNBC.com reported. The Christchurch airport is closed, and rail service has been suspended.
As aftershocks continue to shake the region, half of Christchurch's central business district is without power, Radio New Zealand reported, and water pipes and sewer lines across the area are said to have been ruptured.
Earthquakes on New Zealand's South Island are most often caused by the collision of the Australian and Pacific tectonic plates.