A large 6.3 magnitude earthquake has struck Christchurch, with reports of buildings down and serious injureis, five months after the city was badly damaged by a 7.1 magnitude quake.
Witnesses said there were buildings down all around Cathedral Square in the city, with the church destroyed.
Christchurch resident Sean Scanlon said it was by far the biggest shake since the original September 4 quake. The power was out and phone lines jammed.
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"> EARTHQUAKE VIDEO
Dale Grant from the US Geological Survey explains why the damage of today's Christchurch quake, measuring 6.3 on the Richter scale, is so much greater than that of last year's 7.0 quake.
Christchurch Mayor Bob Parker says today's quake left people in the city council building injured, and he's heard reports of other serious injuries throughout the city.
The US Geological Survey said the temblor was centred five kilometres from the city at a depth of four kilometres.
As more aftershocks rocked the city, Christchurch Hospital was being evacuated, a spokeswoman for the hospital said.
Kay Cowlishaw said there was destruction everywhere.
"There's just water pouring out and sewerage, the whole garage is filled with water. There are cracks in the road."
A visitor to the city, Philip Gregan told AAP over the phone: "It was incredibly violent, very very scary.
"We're all standing out on the street with sirens going off around us.
"Oh no, there's another one," he said while on the phone.
"I want to get out of here."
The cathedral has taken a huge hit, say police, and the airport has been closed.
GNS Science said the quake was centred at Lyttelton at a depth of five kilometres.
The New Zealand Herald reported that the jolt was felt in the capital Wellington to the north and the city of Dunedin to the south.
Residents say it lasted about a minute.
Tarmac on the road was cracked and water mains had burst, flooding the streets with water.
The epicentre of lLast September's quake was 40 kilometres west of Christchurch at a depth of 10 kilometres.
About 100 people were treated at hospital with earthquake-related injuries but no-one was killed.
The city, New Zealand's third largest, has been shaking regularly since, with aftershocks up to 5.1 magnitude recorded.
Nathan, a Melbourne surgeon attending a medical convention in Christchurch, said he had seen major destruction around the city following the quake, which was followed 5-10 minutes later by a strong aftershock.
He feared there would be fatalities, including at the cathedral in the main square where the steeple had been destroyed.
‘‘I’m over here at a convention in Christchurch and just in the middle of a session, you know, the speaker was speaking and suddenly the ground shook, and glass was breaking and it was really quite frightening,’’ Nathan told radio 3AW.
‘‘Fortunately nobody from our convention appears to be severely hurt but there’s a lot of major destruction here in Christchurch.’’
‘‘I don’t know if you know the church in the centre of town, the steeple has fallen over. I’m certainly fearful that there will be some fatalities amongst that, and a lot of the buildings just adjacent to the city square, the awnings of buildings have all fallen down and a lot of buildings around here, it looks pretty shaken up. All the water mains have burst. There’s water seeping up through the roads. It’s a fairly scary place to be right now.
‘‘The road has been buckled up, just like looking at bits of liquorice sort of burst up on the seam. It really is quite incredible.’’
He said buildings had fallen onto cars, while ‘‘lots of second storeys have fallen onto first storeys’’.
‘‘I guess a lot of us now don’t know what to do. Some of us were thinking to go down the hospital to help out but we were told not to leave the area because it’s not safe,’’ Nathan said.
stuff.co.nz, smh.com.au and AAP