Matt Shallcrass was in a car that was rocked from side to side so badly he thought it would roll as buildings collapsed on to people all around him.
The 26-year-old was in High St when the earthquake hit. He watched in horror as buildings collapsed and buried people who were on pavements during the busy lunch period.
"We were driving and buildings just started collapsing all around us, covering people. We watched quite a few people just get buried under the buildings that were toppling over."
He said the people - many of whom were feared dead - were walking directly under the awnings of shops.
They collapsed suddenly within seconds of the shaking first starting. The shaking was so violent he thought the car would roll over.
"The people were walking under the awnings of the shops on the footpath and it just piled on top of them."
Asked how many people he saw trapped, he said: "It was a bit of blur but would be 30 or 40 quite easily. It was in the middle of lunch and we were right in the hub of town."
It was a shocking thing to watch.
"It was kind of weird because we didn't hear anything in the car but just seeing it all happen and getting out and seeing the big dust plume and hearing the noise and everyone screaming ..."
There was so much noise he couldn't hear if anyone was screaming for help under the rubble. "It was pretty noisy in the middle of town and there were people upset and making a bit of noise."
In the minutes after the earthquake many people walked around in an absolute daze.
"There were lots of people in shock. They were crying and supporting each other," he said.
He told the Herald he left the car in the city and tried to help people from the rubble - but there was no sign of anyone to save. "We didn't find anyone. Then the police and rescue crews took over."
They were stopped from searching because floors above them were still unstable. But he did see signs of life when two people emerged unscathed from a partially collapsed building.
"There was a couple in a two-storey building. The front had come off and they appeared from the second storey and climbed down the rubble."
Mr Shallcrass said the sheer power of the earthquake amazed him.
"Just seeing big buildings getting thrown like toys."