The toilet door was too hot to touch and was tightly shut but, with the help of another passerby, they managed to pry it open.
"When we opened the door it was just like a fireball as more oxygen got to it. It was just horrendous, I don't know how anybody could have survived it.''
They managed to extinguish the fire and pull out the man, who by this time was unconscious and badly burnt.
"All his clothes were burnt and he was in a mess.''
The three rescuers poured buckets of cold water over the man until emergency services arrived and took him to Hawkes Bay Regional Hospital, where he is in an induced coma in a critical condition.
There was a jerry can of petrol in the toilet, Mr Smith said.
The hairs on the rescuers' arms were singed by the fire, which was so hot it melted Mr Smith's Crocs shoes and burnt his foot.
Ms Bardell also suffered a burn to her arm.
Sergeant Eden Sewell said the man certainly would have died had it not been for the "heroic'' actions of the rescuers.
"They put themselves at risk, literally. You're talking about a fireball in a very small space and it's certainly pretty dangerous to try and do that.
"They did an awesome job, very heroic.''
Mr Sewell also hoped to track down the passerby who had helped - and who was gone by the time police arrived - so he could commend him for his actions.
A member of the injured man's family had been contacted and police were trying to locate other relatives.
Initial indications were that the fire had been deliberately lit and the man was the only person involved.
