Police and fire crews attend the scene of an explosion on Lappington Road, Otara. Four people were injured in the incident. Police are investigating.

Leftover fumes from petrol sniffing were to blame for an explosion that left four injured, one critically.

Fire investigator Terry Jordan said the Fire Service had ruled the explosion, at a house in south Auckland's Otara on Tuesday, accidental.

It was likely caused by the "fumes from petrol they'd been sniffing earlier on" which were left on the victims' clothes.

LAWRENCE SMITH/FAIRFAX NZ An Otara fire has been ruled an accident, with leftover fumes from petrol sniffing the likely cause.

"They'd attempted to have a cigarette or a smoke or something and when they've done that the fumes on the clothing have ignited."

READ MORE: Four burned in house explosion in Otara, Auckland

Emergency services were called to the house in Lappington Rd at 2.40pm on Tuesday.

RNZ Sniffing petrol and then lighting a cigarette appears to be the near-fatal mistake that has put south Auckland teenage girls in hospital with horrific burns.

Fire Service spokesman Jarron Phillips said four people had received burns in the accident.

All four were taken to Middlemore Hospital, one in critical condition, another serious, and the two others in moderate condition.

Neighbour Chad Tuara said he heard a window smash and a large explosion, then "two girls on fire rolling on the ground".

He tipped water onto them while they screamed in pain.

One of the girl's clothes "had pretty much melted onto her skin", Tuara said.

"Her skin was bubbly, clothes stuck to her skin, screaming."

Counties Manukau police Inspector Kerry Watson said officers were "seeking a fifth person" who had been in the house at the time.

A police spokesperson said enquiries were ongoing on Wednesday morning.