A Westport man has told how he and three others ran for their lives when the Pike River Coal mine exploded at 2.37pm on Wednesday.
The explosion shattered hopes the 29 men trapped underground by a blast six days earlier could have survived.
Gary Bainbridge said he, two other employees of Solid Energy's Stockton mine, and a Pike electrician, were the closest people to the second blast.
They had spent about four hours taking gas samples from a 600mm diameter mineshaft, on a ridge in bush 50 metres from the main ventilation shaft.
Mr Bainbridge, 65, said they were waiting about five metres from the smaller shaft for a helicopter pick-up when they heard a roar.
"It sounded like a huge jet coming. We just had time to get out of it, just run like hell...It was all just split second stuff."
They had sprinted 10 metres down the ridge when an "enormous boom" blasted smoke from the two vents, blotting out the sky.
"I just know nobody could survive that second one (explosion)," Mr Bainbridge said. "You had to be there to realise it."
The air, which had smelled of burning since they arrived two days earlier, filled with soot.
The mine base radioed to check they were safe, then they evacuated the ridge.
"We let them know we were safe and we let them know where we were going."
Pike also evacuated everyone else off the hill, Mr Bainbridge said.
The explosive gas fumes meant a helicopter could no longer fly in to collect them, so the four men lugged their gear down a creek to a clearing.
"We had quite a monstrous struggle with our equipment, which we managed to salvage. We left a wee bit on the hill. It was quite awkward -- scanning equipment, control box, computer, plus our personal gear -- packs and stuff."
A helicopter arrived a couple of hours later and flew them back to base. "I've never seen so many people so happy to see us."
The second explosion vindicated the decision not to send rescue teams in to bring out the 29 trapped miners and contractors, said Mr Bainbridge, a former mines rescuer with 30 years mines rescue experience.
"To me, they made the right decision. Absolutely."
He and Westport's Trevor Shepherd, John Taylor and Allen Morris had been at Pike mine since Monday sampling and analysing gases. The men are members of Solid Energy's Millerton underground investigation team.
Mr Bainbridge said they and their equipment were still available anytime Pike needed them.