Commenting on the anniversary of the disaster, O'Neill told The National newspaper that there was no doubt that the earthquake was one of the worst in the nation's history.
He said the unexpected occurrence made the situation worse as it had been so long since previous earthquakes in the area.
"The devastation was of a scale that had been unimaginable. Villages and their people were lost down sheer mountainsides," he said.
"But one of the most endearing outcomes of this disaster is the way people pulled together to help each other. From villages who themselves had lost homes and loved ones to some of our largest companies and community groups, people got to work very quickly."
O'Neill said so many people should be commended for their efforts to save lives and help rebuild communities.
He told The National that there was still a lot of work to be done and for many people their lives would never be the same.
"We will continue with restoration operations in the affected areas, and lessons will be learnt from the disaster.
"This disaster also occurred at a time when our country was faced with lower commodity prices and global uncertainty, and it was anticipated the economic cost of the disaster would be more than was ultimately the case."
O'Neill said there was a slight negative economic impact, but the manner in which business operations came back online lessened this.