He had met with Pike River Coal chief executive Peter Whittall after a devastating explosion in the mine on November 24 extinguished any hope for survivors.
Mr Whittall had told him the dead miners were "his men" and asked to handle the announcement to families.
But Mr Whittall began the meeting with news from earlier that day when authorities were considering launching a rescue operation.
Families clapped before Mr Knowles interjected and told them the men were dead.
"I've never seen such an outpouring of grief," Mr Knowles said.
"It was not the way it should have been given, and I apologise to each of you."
Mr Knowles said informing the families all hope had been lost was the most difficult day of his life.
He said everyone on the rescue and recovery team was also devastated at the news of a second massive explosion at the mine.
"All the people that were working on that day were doing their best."