A powerful magnitude 7.8 earthquake struck off New Zealand's Kermadec Islands, triggering a tsunami in the region, the U.S. Geological Survey and the U.S. Pacific Tsunami Center said on Wednesday.

The quake, initially reported as a magnitude 7.9, triggered a tsunami warning for New Zealand, the Kermadec Islands and Tonga, the U.S. Pacific Tsunami Center said.

"Sea level readings confirm that a tsunami was generated. This tsunami may have been destructive along coastlines of the region near the earthquake epicenter," the U.S. Pacific Tsunami Center said in its warning.

It struck at 7:03 a.m. on Thursday (1903 GMT on Wednesday) at the epicenter, 131 miles (211 km) east of Raoul Island, part of the Kermadec archipelago, and was only 30 miles (48 km) deep, the USGS said.

The Pacific Tsunami Center said waves were 2.2-2.7 feet (68-84 cm) high around Raoul Island.

The U.S. Pacific Tsunami Center said it estimated that waves would reach East Cape in New Zealand within two hours and Auckland within three hours of the quake.

The Kermadec Islands, which are New Zealand's northernmost inhabited islands, are 500 miles (800 km) northeast of New Zealand's North Island.