Some screamed for help from inside collapsed buildings, others tapped on the rubble to communicate with rescuers and one managed to call her daughters and say goodbye.

Search teams worked desperately Wednesday to rescue the more than 100 people trapped by a deadly earthquake in New Zealand, using search dogs, heavy cranes, earth movers and even their bare hands.

At least 120 survivors were pulled from the crumbled concrete, twisted metal and huge mounds of brick nearly a day after the quake struck the city of Christchurch, but officials also raised the death toll to at least 75, with 300 others listed as missing.

The death toll is expected to rise further, ranking the 6.3-magnitude earthquake among the island nation's worst in 80 years.

"There are bodies littering the streets, they are trapped in cars, crushed under rubble and where they are clearly deceased our focus ... has turned to the living," police Superintendent Russell Gibson said.

Prime Minister John Key declared a state of national emergency Wednesday, giving the government wider powers to take control of a rescue and recovery operation that was growing by the hour.

Key told reporters that Christchurch was "a scene of utter devastation" in the aftermath of the quake.

"We may well be witnessing New Zealand's darkest day," he said.

Eighteen hours into the disaster, emergency workers were still trying to reach the more than 100 people who were missing and presumed buried after the quake.

One woman spoke to a New Zealand TV station from under her desk, where she had been pinned when the office building where she worked collapsed.

"I rang my kids to say goodbye," Ann Voss told New Zealand's TV3 from underneath her desk.

"It was absolutely horrible. My daughter was crying and I was crying because I honestly thought that was it. You know, you want to tell them you love them don't you?"

Voss, who was still waiting to be rescued when she spoke to the TV station, said she could hear others who had survived the quake.

"I'm not going to give up," Voss said. "I'm going to stay awake now. They better come and get me."

She was later rescued.

Tony Wallace, a spokesman for the New Zealand government, said the placement and severity of the 6.3-magnitude quake caught the country's second-largest city by surprise, striking in the middle of the workday.

"The earthquake was situated just right below Christchurch…and it was quite shallow," Wallace told CTV News Channel by telephone from the city of Wellington.

Witnesses say the quake hit without warning, toppling telephone and power lines, collapsing the spire of the city's historic stone cathedral and dropping many tall buildings in the downtown, leaving victims with no time to escape.

Web designer Nathaniel Boehm was eating his lunch outdoors when the rumbling started and watched in shock as the roofs of some buildings dropped down to street level, burying people below.

"People were covered in rubble, covered in several tons of concrete," Boehm told The Associated Press. "It was horrific."

More than 400 rescue workers were joining the search, including teams from Australia, Singapore, Taiwan, the United States and Britain, and are concentrating their search on a dozen buildings that collapsed or were badly damaged by the quake.

In one of the worst, a camera inserted into the rubble showed images of people still alive, Christchurch Mayor Bob Parker said.

Some survivors emerged without a scratch, while others had to have a limb amputated before they could be freed.

Mall worker Tom Brittenden said he helped pull victims from the rubble in the immediate aftermath of the quake.

"There was a lady outside we tried to free with a child," Brittenden told National Radio. "A big bit of concrete or brick had fallen on her and she was holding her child. She was gone. The baby was taken away."

Military units patrolled near-empty streets disfigured by the huge cracks and canyons created in Tuesday's earthquake, the second powerful temblor to hit the city in five months.

A 7.1-magnitude earthquake hit the city in September, but that quake was much farther away.

The epicentre was at a relatively shallow depth beneath Christchurch, so many people were within 10 to 20 kilometres of the rupture.

Firefighters climbed ladders to pluck people trapped on roofs of office towers to safety. Plumes of grey smoke drifted into the air from fires burning in the rubble, and helicopters used giant buckets to drench them with water.

Thousands of people in the city moved into temporary shelters at schools and community halls. Others, including tourists who had abandoned their hotels, huddled in hastily pitched tents and under plastic sheeting as drizzling rain fell, while the Red Cross tried to find them accommodation.

While the Department of Foreign Affairs said early Tuesday it had no reports of Canadians affected by the quake, officials with the Canadian High Commission in Wellington are ready to help if needed.

Anyone seeking information on Canadians believed to be in New Zealand can contact Foreign Affairs at 1-800-387-3124.

With files from The Associated Press and The Canadian Press