The Prime Minister has acknowledged the feelings of sadness, mixed with frustration, being felt by many in Canterbury today.

John Key spoke at this morning's Latimer Square Civic Memorial Service, where hundreds went to honour those killed in the earthquake 12 months ago.

He says February 22 began as just another summer day in Canterbury and people were just going about their business, but at 12:51 everything changed.

"It twisted the buildings, tore up roads, destroyed homes and shook us to the core. Worst of all it stole 185 loved ones from us."

Mr Key talked about how Latimer Square was completely different today to was it was a year ago, with emergency services around the place.

"It was a New Zealand I have never seen before."

He has pledged to build a new Christchurch but told those gathered that there is a long journey to go for many.

"It'll take time to recover from the fourth largest earthquake insurance event ever experienced in the world. An earthquake so severe that in some place the vertical shaking was more than the force of gravity," Mr Key says.

"In part today is a day to look forward, to dare to dream what a new, vibrant and confident Christchurch will be like, but today is a time to pause and reflect."

He also paid tribute to those who stepped up to help others after the quake.

"February 22 will forever be one of the darkest days in this proud nation's history, it will also be a day when in the worst of times the best of human spirit was on display. That spirit is something that no earthquake can ever take away," he says

"People who, despite being personally affected by the quake, dropped everything to help the person beside them or answer the call of duty.

"(The quake) couldn't break the spirit you are famous for."

Christchurch mayor Bob Parker says nothing in could've shown Canterbury what was to happen a year ago.

"We had been through one earthquake, it was difficult but we believed we were on a road to recovery, then on this day one year ago everything changed and it will never be the same again."

He also highlighted the spirit of the thousands who helped with the quake response and thanked those who came from afar to help.

The service began with a Maori blessing and contained music from the New Zealand Army Band and ended with the families of the victims being taken on a bus tour through the city's red zone.

Photo: A man waits for the Latimer Square memorial to begin (Getty Images)