The flat was beside the house of the injured woman's brother-in-law, Nuhaka volunteer fireman Ian Barber and the impact also smashed his windows and cracked the wall of his house.
"I ran around the house and screamed at her to get out of the house," he said. "She was dazed and staggering around. I shouted at her to come towards me."
She scrambled to him through the burning wreckage.
"I put her in the shower and told my wife to keep her in there and I got the hose and put it through the window to put extra water on her."
Mr Wesche, who was already awake at his home 200m away, was about to make a cup of tea when he heard the explosion. The noise was so loud and the jolt of his two-storey house so great he wrongly assumed the explosion was at his next-door neighbours and ran to the fenceline.
"When I looked over my shoulder I could see a big plume of smoke," he said.
He drove 600m to the Nuhaka Fire Station where his crew had assembled.
"The little bach was flattened. We had to make sure it wouldn't spread to the house."
The rescuers at first thought the woman's son was in the house with her but he was found safe, Mr Wesche said. "Thank God he was asleep back in her home."
The remaining walls and roof structures soon collapsed.
"If Ian hadn't got there she would have been buggered," he said. "He probably saved her life."
Mr Barber denied being a hero.
"I was just doing what anyone else would have done. Because I am a fireman I knew I shouldn't go into the house alone so I called her out."
He said it was lucky there was no wind at the time or the flames might have claimed Mr Barber's house.
"It was thanks to Wairoa and Mahia [fire services] who were here quick with their tankers that the flames did not spread."
Mr Wesche said the fire service and gas company were investigating. A large gas cylinder was lying on the ground beside the building.
"This is a wake-up call. The building was only two years old."
St John ambulance secured a landing spot for the Lowe Corporation rescue helicopter at a school so it could take Tia Ropitini to Hawkes Bay Hospital. She was later transferred to the Intensive Care Unit at Middlemore Hospital. She was in a serious but stable condition yesterday.