A strong earthquake measuring 7.8 on the Richter scale struck off Southland, New Zealand's lower South Island, on Wednesday evening.

The earthquake was centered 100 km northwest of Tuatapere in western Southland, and was 12 km deep, the New Zealand Institute of Geological and Nuclear Science (GNS Science) reported.

GNS Science said earlier the quake was measured at 6.6 magnitude.

The earthquake, which was recorded at about 9:22 p.m. (09:22 GMT), was felt across Southland and Otago region. Local residents said the earthquake lasted several minutes.

A 6.1 magnitude aftershock was also reported at 9:41 p.m. (09: 41 GMT).

The Hawaii-based Pacific Tsunami warning center has issued a non-expanding regional warning for a possible tsunami for part of the Pacific near the earthquake.

Local residents have been advised to keep listening to the radio.

Vince Cholewa of the Emergency Management Center said GNS scientists were working with their U.S. counterparts to reconcile measurements of the quake and the tsunami risk, Radio New Zealand reported.

There were reports of cracks in buildings in the Tuatapere area, and power was out there for a short time.

There were also reports of items falling off a supermarket shelf in Queenstown and walls in Invercargill. It was also felt in Dunedin.

New Zealand Civil Defense in Southland has activated the region 's Emergency Operations Center. They have not received reports of casualties so far.

The GNS places the quake epicenter in deep water close to Dusky Sound in Fiordland, a considerable distance from any township.

Police in the southern city of Invercargill said they have checked with residents in Tuatapere and so far there have been few damage reports. The full extent of the damage will not become apparent until daylight.

Power was still out in parts of Southland at 11:00 p.m. after the quake.

Ganesh Singh from Powernet said power lines were broken in the quake and supply has been cut to more than 150 homes at Otatara on the outskirts of Invercargill, according to Radio New Zealand.

(Xinhua News Agency July 15, 2009)