WELLINGTON - A strong earthquake killed at least 65 people in New Zealand's second-biggest city of Christchurch on Tuesday, with more casualties expected as rescuers worked into the night to find scores of people trapped inside collapsed buildings.
It was the second quake to hit the city of almost 400,000 people in five months, and New Zealand's most deadly natural disaster in 80 years.
"We may well be witnessing New Zealand's darkest day...The death toll I have at the moment is 65 and that may rise," said New Zealand Prime Minister John Key, who had flown to his home town of Christchurch, where he still has family.
The 6.3 magnitude quake struck at lunchtime, when streets and shops thronged with people and offices were still occupied.
Rescuers, working under lights in rain, focused on two collapsed buildings: a financial-services office block in which four stories had pancaked on top of each other, and a TV building that also housed an English-language school.
Twelve Japanese students at the school were believed to be missing, an official in Japan told Reuters.
Trapped survivors could be heard shouting out to rescuers from the TV building. Local media say as many as a dozen or more people could still be inside. Relatives of those feared trapped kept a vigil outside the building as rain began to fall.
A woman freed from a collapsed building said she had waited for six hours for rescuers to reach her after the quake, which was followed by at least 20 aftershocks.
"I thought the best place was under the desk but the ceiling collapsed on top, I can't move and I'm just terrified," office worker Anne Voss told TV3 news by mobile phone.
Christchurch Mayor Bob Parker described the city, a historic tourist town popular with overseas students, as a war zone. He told local radio that up to 200 people could be trapped in buildings but later revised that estimate down to about 100 or so.
"It is a tragedy that is unbelievable," he said.
It was the country's worst natural disaster since a 1931 quake in the North Island city of Napier that killed 256. Christchurch Hospital saw an influx of injured residents.
"They are largely crushes and cuts types of injuries and chest pain as well," said David Meates, head of the Canterbury Health Board. Some of the more seriously injured could be evacuated to other cities, he added.
All army medical staff have been mobilized, while several hundred troops were helping with the rescue, officials said.
Christchurch has been described as a little piece of England.
It has an iconic cathedral, now largely destroyed, and a river called the Avon. It had many historic stone buildings, and is popular with English-language students and also with tourists as a springboard for tours of the scenic South Island.
Emergency shelters had also been set up in local schools and at a race course as night approached. Helicopters dumped water to try to douse a fire in one tall office building, while a crane was used to help workers trapped in another office block.
"I was in the square right outside the cathedral — the whole front has fallen down and there were people running from there. There were people inside as well," said John Gurr, a camera technician who was in the city center when the quake hit.
"A lady grabbed hold of me to stop falling over...We just got blown apart. Colombo Street, the main street, is just a mess...There's lots of water everywhere, pouring out of the ground," he said.
Streets turn into quicksand
Christchurch is built on silt, sand and gravel, with a water table beneath. In an earthquake, the water rises, mixing with the sand and turning the ground into a swamp, swallowing up roads and cars.
TV footage showed sections of road that had collapsed into a milky, sand-colored lake beneath the surface. One witness described the footpaths as like "walking on sand."
Unlike last year's even stronger tremor, which struck early in the morning when streets were virtually empty, people were walking or driving along streets when the shallow tremor struck, sending awnings and the entire faces of buildings crashing down.
Police said debris had rained down on two buses, crushing them, but there was no word on any casualties.
The quake hit at 12:51 pm at a depth of only 2.5 miles, according to the U.S. Geological Survey.
Quake could damage already frail economy
Fears that the quake could dent confidence in the country's already fragile economy knocked the New Zealand dollar down by about 1.8 percent from late U.S. levels to $0.75.
Westpac Bank raised the possibility that the central bank could cut interest rates over the next few weeks in a bid to shore up the economy, while other banks pushed out their expectations for the timing of the next rate increase.
ANZ now expects the central bank to keep rates on hold until the first quarter of 2012.
Shares in Australian banks and insurers, which typically have large operations in New Zealand, fell after the quake.
The tremor was centered about 6 miles southwest of Christchurch, which had suffered widespread damage during last September's 7.1 magnitude quake but no deaths.
New Zealand sits between the Pacific and Indo-Australian tectonic plates and records on average more than 14,000 earthquakes a year, of which about 20 would normally top magnitude 5.0.
(Additional reporting by Bruce Hextall, Michael Smith and Cecile Lefort in Sydney; Saika Takano in Tokyo; Writing by Mark Bendeich and Ed Davies; Editing by Daniel Magnowski & Kim Coghill)