A magnitude-6.8 earthquake off New Zealand's east coast rocked much of the country on Thursday, emergency officials said.

No immediate tsunami warning was triggered at the Pacific Tsunami Warning Center in Hawaii by the offshore temblor. There were no immediate reports of casualties.

The quake, centered in the Hikurangi undersea trench off North Island, hit at 8:55 p.m. and occurred 25 miles below the surface, the GNS Science geological agency reported.

Detailed earthquake information and maps from the USGS

The agency said the quake was located at sea some 30 miles from the coastal city of Gisborne.

The U.S. Geological Survey said the quake had a magnitude of 6.6.

Police in Gisborne said there had been damage to buildings and roads in the city.

"Some roofs have collapsed; we are still trying to ascertain the amount of damage (to the city) but we have no injuries," police inspector Wata Shepherd told The Associated Press.

At least one main road had a large hole in it and some central city streets had been closed in the wake of the temblor, with power lines down in some area, he said.

Callers to a radio station told of television sets and other household appliances being tossed over, kitchen cupboard contents smashing to floors. But power cuts had prevented them from fully assessing damage to their homes, they said.

New Zealand sits above an area of the earth's crust where two tectonic plates are colliding and records more than 14,000 earthquakes a year — but only about 150 are felt by residents. Fewer than 10 a year do any damage.

The Geonet Web site, operated by GNS Science, said the quake was felt widely but most strongly along the east coast of North Island.