A third explosion has occurred at the Pike River Coal mine near Greymouth.
The explosion happened at 3.39pm on Friday, just five minutes before a one-minute silence at the mine. That was held at precisely the time one week ago the first explosion struck.
Pike River Coal's chairman John Dow confirmed the incident after the news had been leaked to other media.
He told a hastily-convened news conference in Greymouth the explosion lasted 20 seconds and was smaller than both the initial explosion and the one on Wednesday that extinguished all hope of finding 29 mine workers trapped underground alive.
He also said the explosion was discovered by CCTV.
Mr Dow said the families of the men had not been told of the event first after the information was officially made public on other news websites.
Also on Friday, Mr Dow announced the company will be running its own independent enquiry into the disaster.
It will come on top of at least four other investigations, including a commission of inquiry.
Mr Dow says the company will feed information it finds into the other inquires, so that everybody is working with same objective, to get to the truth, and make sure it never happens again.
However, he says he believes the damaged mine site still has value and can be rebuilt.
He says the biggest challenge it faces is assessing the damage sustained to the mine's underground infrastructure.
Mr Dow says the company has two business interruption insurance policies to the value of $100 million and work to lodge claims against them is under way.