Major quake strikes off New Zealand's coast; tsunami warning issued

(CNN) - New Zealand is under a tsunami warning after a major earthquake with a magnitude of 7.8 struck Wednesday off the west coast of its South Island, according to the U.S. Pacific Tsunami Warning Center.

Twenty minutes later, a 5.8-magnitude aftershock struck the same region, according to the U.S. Geological Survey, which measures earthquakes around the world.

The initial quake struck around 8:22 p.m. local time (9:22 a.m. UTC/5:22 a.m. ET) and its epicenter was located 95 miles (150 km) west-northwest of Invercargill, according to the USGS.

The aftershock struck in about the same area, according to the USGS.

The tsunami warning, which was issued as a precaution, applies only to New Zealand. The warning center said it is not known if any strong ocean waves were actually generated by the quake.

The warning says major cities in New Zealand, including Wellington and Auckland, could be affected by a potential tsunami in the next four to five hours after the initial quake.

So far, there have been no reports of major damage.

The temblor shook buildings in Queenstown - located about 110 miles northwest of the epicenter - and scared residents who ran into the streets, according to the New Zealand Herald.

The quake, which was felt across South Island, downed power and phone lines, the newspaper reported.

"It wasn't very violent, more of a rolling feel," Simon Darby, a resident of the inland town of Wanaka, told the Herald. "But it had a power about it - I ran straight outside into the carpark."