Only 10 minor injuries were reported in the port city of Gisborne, which was hit hardest by the quake and suffered the most property damage, although it was felt all over the country, officials said.

The magnitude 6.8 quake, which struck at 8:55 p.m. (10:55 p.m. last night Hawai'i time) was centered in the Hikurangi undersea trench off North Island, 25 miles below the surface, and about 30 miles southeast of Gisborne, the GNS Science geological agency reported.

The U.S. Geological Survey recorded the quake at magnitude 6.6.

The temblor did not trigger a tsunami warning at the Pacific Tsunami Warning Center in Hawai'i.

Police cordoned off a large part of Gisborne's central business district until engineers could inspect damaged buildings and ensure they were safe to enter, said senior police Sgt. Moira Brown as dawn broke Friday.

"We have got a lot of damage and are still assessing the situation," police inspector Waata Shepherd said. "Some roofs have collapsed. We are still trying to ascertain the amount of damage."

The central city area had been "locked down" because of the damage, he said.

Power lines were down in some areas, and the quake had left a huge hole in one of Gisborne's main roads, he added.

Mayor Meng Foon said the fire department put out 10 small blazes, and water and sewage systems were still working.

Callers to NewstalkZB radio said the quake sent TV sets and other appliances crashing to the floor, but that the lack of power made it difficult to assess the damage to their homes.

Gisborne District Council spokesman Vance Walker told TVOne News that three historic buildings had collapsed in the center of the city, and a damage assessment was still under way.

Ministry of Civil Defense and Emergency Management spokesman Vince Cholewa confirmed three buildings collapsed. "As far as we are aware, there are no injuries in those buildings," he said.

Jim Green, chief executive of Gisborne's Tairawhiti District Health Board, said no one had been admitted with injuries.

The National Crisis Center was activated to assist local agencies dealing with the quake's aftermath.

Vulcanologist Dr. Warwick Smith of GNS Science said the quake was not strong enough to spark a tsunami off the coast.

"My judgment call ... was that 6.8 wasn't big enough for a tsunami," he told National Radio. "The ocean floor has to either be uplifted or subside to move that water, and 6.8 isn't big enough."

One caller, who identified himself only as Brian, said his family sheltered in doorways as the quake rocked Gisborne. "That was a ride and a half. It was freaky," he said.

Murray McPhail, who lives about six miles outside Gisborne, said the quake caused waves in his swimming pool.

"Stuff came out of cupboards, bottles fell off walls, ornaments fell," McPhail told NewstalkZB. "It was pretty violent. It was certainly a decent shake."