Moments later St John Ambulance staff took her from her home and she watched events unfold from the ambulance.
"I could hear the firemen yelling, 'Open the door, open the door.'
"When they did get the door open the flames just burst out ... then they brought him out and poor Mark was just lying out there."
She said a social worker visited Mr McCarthy about two weeks ago to assess his living arrangements and see if he needed additional help or care.
"After visiting him she felt he was unable to look after himself," said Ms Williams.
Another neighbour, who asked not to be named, said Mr McCarthy broke a hip while walking down stairs to the rear of his unit around Christmas last year.
She said he spent several weeks at Waikato Hospital and was not the same when he returned.
"He wasn't that great before his fall and when he came back, well, he shouldn't have come back because he needed care.
"But I don't think he wanted to go [into care] so it's just tragic, it's very sad."
Waikato senior fire risk management officer Kevin Holmes said the blaze was well alight when Te Aroha firefighters arrived.
He said it appeared the fire started when items on a small table near a portable gas heater in the lounge caught alight.
Mr Holmes said Mr McCarthy activated his personal medical alarm but could not speak to those monitoring it.
"He's been overcome with smoke to the point where he's collapsed," he said.
Mr McCarthy's sister-in-law Rose McCarthy said he was one of 12 children but had several half-siblings.
He also had two sons and two daughters whom she believed were in their 40s.
She said he had been living in the the flat for at least 10 years but "should not have been on his own" as he was barely mobile and used a walker to help him get around.
Mr McCarthy's death has been referred to the coroner.
