New Zealand authorities declared a civil emergency in a central city Friday when several of its older buildings collapsed due to a magnitude 6.8 quake that jolted much of the country.

Thursday's quake off New Zealand's east coast caused damage to Gisborne's infrastructure but no serious injuries. At least 10 people were treated for minor injuries, officials said.

The quake, centered in the Hikurangi undersea trench off North Island hit at 8:55 p.m. local time (0755 GMT) at 25 miles below the surface, the GNS Science geological agency reported. It was located about 30 miles southeast of the coastal city.

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

As part of the emergency ordinance, police cordoned off the city's central business area to ensure no serious casualties occured in damaged buildings, senior sergeant Moira Brown of Gisborne police said as dawn broke in the area early Friday.

"Our role is to cordon the area and prevent everybody, including shop owners and retailers from going into that CBD (central business district) till buildings and structural damage have been checked by engineers," Brown said.

"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.

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

The National Crisis Center was activated to assist local agencies dealing with the quake's aftermath. The emergency ordinance means central government assistance will be speeded up, officials said.

The temblor did not trigger any tsunami warning at the Pacific Tsunami Warning Center in Hawaii.

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 (sea) water, and 6.8 isn't big enough."

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.

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

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.

Gisborne Mayor Meng Foon said things "flew out of the cupboards" at his home as the quake rattled the region.

"A number of buildings have collapsed and I can see dents in a number of buildings," he told National Radio, adding that collapsed walls and smashed glass littered the streets.

The fire department had put out 10 small fires, but outlying areas had still to report major damage, he said.

The Geonet Web site operated by GNS Science had at least 1,400 reports of the quake from people across much of New Zealand, but said its impact was particularly felt along the east coast of North Island.