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(CNN) -- A man trapped on the 12th story of a Christchurch building on Tuesday told how aftershocks rumbled through the damaged building, rattling the nerves of the 19 other co-workers trapped on the same floor.
"Every aftershock sends us scrambling, it doesn't take much to set us off," Gary Moore told CNN by phone from the 17-story Forsyth Barr building in Christchurch where a 6.3-magnitude earthquake ripped through the city at lunchtime leaving at least 65 people dead.
"Both the stairwells have collapsed and we are just looking into a void," Gary Moore told CNN as he remained trapped in the 17-story building. "We're fine but we are badly shaken. We're just playing the waiting game and letting loved ones know we're okay.
"We watched from the building as our cathedral collapsed and a five-story building. We've got 10 people here from our office and another 10 people from an adjoining office.
"Someone has written on the pavement that help is on its way. We're doing our best to jolly people along," he said. "The language was a bit rich when it first hit."
Local network footage showed a large crane with a steel cradle taking survivors from the 17th floor of the building. Helicopter footage showed others on the roof.
Earlier witnesses described how the earth buckled, sending terrified residents into the street as boulders fell from cliffsides, buildings collapsed and roads cracked.
"It felt like I was running on jelly," Gavin Blowman said. "We saw a giant rock tumble to the ground from a cliff -- a rock that had been there for millennia. It fell on the RSA (Returned Services Association, a veterans' association) building -- it was terrifying." He said there were now fears that a tsunami could hit in the wake of the quake and that he and 20 other people were trying to get to higher ground.
One witness who escaped a collapsed office said he was lucky to have been just two meters from edge of the building when it came down, allowing him to escape.
"The floor just went out from beneath you and the ceiling came up to meet it," he said.
Another witness described how her building collapsed, taking her from the fifth floor to ground level.
"The building opened to one side -- I could feel the air coming in," she said. Another witness said the quake struck so quickly "there was no time to react."
New Zealand's Prime Minister John Key said New Zealand was looking at "its darkest day".
Deputy Prime Minister Bill English said that phone lines were operational but overloaded which was "understandable given the anxiety" of people trying to get in touch with relatives. He requested that people send text messages rather than call to keep lines open for emergency services.
"The government is shaping up to deal with something larger and more devastating than the September earthquake," English said.
Peter Shadbolt contributed to this report.