WELLINGTON, New Zealand - A strong earthquake struck New Zealand last night, toppling at least three older buildings in a coastal city on North Island, sparking small fires and forcing authorities to declare a state of emergency.

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

The magnitude 6.8 quake, which struck at 8:55 p.m. (2:55 a.m. in Philadelphia) 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 Hawaii.

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 today.

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

Power lines were down in some areas, and the quake 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 working.

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.