|John Key, the prime minister, has warned that the death toll from Tuesday's quake in Christchurch could rise [Reuters]
Rescue teams in New Zealand are working around the clock to find people trapped under collapsed buildings after an earthquake struck the city of Christchurch, killing at least 65 people.
John Key, the prime minister, said "we may be witnessing the the country's darkest day" as he warned that the death toll from Tuesday's 6.3 magnitude quake could rise.
"This is a community that is absolutely in agony," he said.
Around eight or nine buildings had collapsed, he said, including the spire of the iconic stone Christchurch Cathedral, which toppled into a central city square.
Bob Parker, Christchurch mayor, declared a state of emergency and ordered people to evacuate the city center.
Video footage showed some multi-storey buildings collapsed in on themselves, while walls of some others collapsed into the streets.
The streets of the central city district were strewn with bricks and shattered concrete as thousands of dazed, screaming and crying residents wandered through them.
Meanwhile, groups of people helped victims, clutching bleedings wounds, and others were carried to private vehicles in makeshift stretchers fashioned from rugs or bits of debris.
Parker said: "We are looking out there on the basis that all of our people there are ok and we are going to get them out but we have to be realistic. This is unprecedented for our city.
"Tonight, our focus is on rescue, recovery is something that we will start thinking about after this first crucial step is over."
He advised the residents of Christchurch, New Zealand's second largest city, to "save water and not use phone lines so much as the phone lines are already overloaded.
"Look after yourself, your families, your neighbours. We are all frightened, we are all traumatised, get together and support each other and remain calm.
John Carter, New Zealand's civil defence minister, said that the government is boosting the number of personnel for ongoing rescue operations.
"The search and rescue teams from New Plymouth and Auckland will be down and operating in the next four or five hours.
"And of course the police in the meantime already have teams of people out there working to go through the damage to try and help and assist where they can," Carter said in a news conference.
Some units of the New Zealand army that were in the city for an exercise, have also been activated to aid with rescue operations.
Speaking to Al Jazeera, Hamish Clark, TV3 correspondent from New Zealand, said the prime minister had told him earlier that, "there were 350 military on the ground, another 250 on the way, 180 police and another 200 on the way".
The airport was closed and Christchurch Hospital was evacuated briefly.
"The airforce is at the airport, and we have help from Australia and America to help us evacuate victims who can't be dealt with in Christchurch," Clark said.
Power and telephone lines were knocked out, and pipes burst, flooding the streets with water. Some cars apparently parked on the street were buried under rubble.
Anne Johns, a Christchurch resident, told Al Jazeera about her experience of the earthquake: "I was in, what is regarded as the safest building in town, the New Christchurch Art Gallery.
"A lot of the glass did break in the building and we went outside to find a party of school children and there was lots of smoke outside."
BP Oil New Zealand has closed its Christchurch service stations subject to inspection of ground based tanks and pipes after the earthquake.
They were shut as a precaution after either loss of power or damage to some forecourts.
The US Geological Survey said the temblor was centered five kilometers from the city at a depth of 4 kilometers.
An earthquake in September last year wrecked hundreds of buildings in the city, and caused an estimated $3 billion in damage. A strong aftershock in December caused further damage to buildings.
Bill Fry, a Wellington-based seismologist, told Al Jazeera: "The ground definitely shook more than it did in September, the duration was less but it shook more violently.
"We expect aftershocks in the coming days so the buildings will be susceptible to more damage."
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 and swallowing up sections of road and entire cars.
TV footage showed sections of road that had collapsed into a milky, sand-coloured lake right beneath the surface as one witness described the footpaths as like "walking on sand".
Christchurch is home to about 350,000 people and is considered a tourist centre and gateway to the South Island.