Miner 'Ran For His Life' From Flooded Colliery
Around 650,000 gallons of water, enough to fill an Olympic swimming pool, gushed into the area where explosives were being used to extract coal from a seam.
Nigel Evans, who operated the Gleision colliery's conveyor belt, said he ran as fast as he could and "did not look back".
Pit boss Malcolm Fyfield managed to escape after crawling through dirt and sludge.
He and former mine owners MNS are on trial at Swansea Crown Court, where both deny manslaughter charges.
Mr Evans said his colleague David "Jake" Wyatt had shouted at him and was "visibly panicking and running".
The miner, who had worked at the colliery for just three days, told the court: "I remember getting a call from Jake saying they were about to fire.
"It all went quiet for a minute and I started to load supplies on the belt to send up to them.
"I heard a gushing wind ... that was a bit unusual.
"Then I saw Jake and his light was shaking furiously. I knew something was wrong straight away."
He added: "(Jake) was visibly panicking and running. He was shouting for me to run. So I just ran out of the main drift. I didn't look back. I was going as fast as I could."
As he approached the surface, Mr Evans glanced back and noticed his colleague had stopped.
"He had hurt his back and was out of breath and there was a body of water that had stopped a couple of metres from him," Mr Evans said.
Once Mr Wyatt had escaped the mine and the emergency services had been called, Mr Evans went back into the shaft, where he shouted for his colleagues.
Philip Hill, 44, Charles Breslin, 62, David Powell, 50, and Garry Jenkins, 39, all died in the tragedy on September 15, 2011.
Mr Evans said Fyfield looked "pretty rough" in the moments before he was rushed to hospital.
"He was out of breath, cold, shaking and wet," he said. "He was in shock and bleeding to his forehead.
"I asked him where the boys were and he said to me: 'They've gone'."
Fyfield denies he was negligent in his duties and insists he carried out regular safety inspections at the colliery.
The trial continues.