©Agence France-Presse
Penny Walsh checks the damages in the local library following a powerful earthquake in Gisborne, New Zealand, 21 December 2007. A state of emergency was declared for the centre of the eastern New Zealand city of Gisborne after a powerful 6.8 earthquake flattened buildings and caused widespread damage.

Aftershocks continued to rattle the eastern New Zealand city of Gisborne Friday after a powerful 6.8 earthquake smashed buildings and left a gaping hole in a street.

No major injuries were reported after Thursday night's quake, which was felt throughout much of New Zealand, although many people had been Christmas shopping in the city area when it struck.

The centre of Gisborne was cordoned off Friday and a state of emergency declared as engineers checked the safety of commercial buildings in the city of 42,000 on the east coast of New Zealand's North Island.

Gisborne District Council spokesman Vance Walker said an apartment building and two shops had partially collapsed and roofs and awnings had caved in.

Eleven people were treated at Gisborne hospital's emergency department for minor injuries, authorities said.

Aftershocks with a magnitude of 4.5 and 4.2 shook the area Friday morning, following the initial quake at 8:55 pm (0755 GMT) on Thursday, which was centred about 50 kilometres (31 miles) from Gisborne, government GNS Science seismologists said.

Reports said most of the major structural damage appeared to be limited to larger old buildings, although many residents reported damage to belongings flung across rooms in their homes.

Following the quake, Kathleen Munn, who lives just outside the city, said the shaking was "horrifying".

"The roof started creaking and the house started shaking, so I grabbed onto the doorway and the house started rocking from side to side," she told Radio New Zealand.

"The books all jumped off the bookcase and the bottles all jumped off the table."

"I thought the house was going to fall down. It was very, very frightening. I felt terrified."

A central city resident, Tim Lewis, who was in a van when the quake struck, said plate glass windows shattered and verandahs collapsed along the main street.

"People were falling down along the main street," he told the Dominion Post newspaper.

"I thought my van was going to flip. It was like there were people on either side rocking the van."

GNS Science seismologist Warwick Smith said further aftershocks were expected, but most would be minor.

"It's hard to say exactly how long they'll go on for, but we'll be recording them for weeks," he said.

There were reports the quake was felt more than 1,000 kilometres (620 miles) away in the South Island city of Dunedin.

Gisborne civil defence controller John Davies told Radio New Zealand some Gisborne residents scrambled for higher ground after the initial quake, fearing a tsunami, although no warning was issued.

Davies said engineers were expected to complete an initial examination of the damage by the middle of Friday.

"We've had three roof cave-ins or partial cave-ins overnight and there is substantial damage to some buildings," he added.

"Other buildings have come away from it extremely well. There has been very little damage reported to houses and it appears to be mainly damage to older substantial buildings."

Several minor fires were reported late Thursday, but they were quickly brought under control, and a gaping hole appeared in a central city street.

Civil Defence Minister Rick Barker was travelling to Gisborne Friday to inspect the damage.