Stuart Osman, 47, of Dubbo as well as Ross Bodkin, 41, Michael House 33, and Colin Lloyd Jones, 41 died when millions of tonnes of ore and earth suddenly collapsed, leading to a catastrophic air blast.

More than 180 people, including family members, past and present employees, local councillors and community members, came together in Cooke Park for a memorial service at 3pm - the same time the incident occurred 20 years ago - to stop and remember the men who lost their lives that day.

Northparkes Mines operations manager Rob Cunningham, who was an underground team leader at the time of the air blast, shared his memories from the day, including a poem dedicated to the four men.

"This event is a black day in the history of Northparkes that is never forgotten - this day reshaped the way we approach safety, mine designs and critical control monitoring," he said.

"I am personally driven every day to prevent the past and be better tomorrow.

"Please spare a thought for all the family and friends that were impacted by this tragedy. Our thoughts and wishes are with you.

"I am sorry that these four good men never made it back to their families 20 years ago."

Northparkes managing director Hubert Lehman was also among those who spoke at the commemorations.

"To all the families whose lives will never be the same as a result of the air blast we think of you every day," he said.

"All four men were exceptional people who had so much to offer but never returned home from work that day.

"We will continue to remember these men every year and share what we learnt from that day to help prevent it from ever happening again."

The ceremony concluded with family members unveiling a chair dedicated to the memory of Ross, Michael, Stuart and Colin.

The chair will be installed on Bushmans Hill Reserve, next to the existing memorial rock.