The gas-powered device blew a massive hole through the roof of the house and started a fire which spread to neighbouring properties.
The school friends, who are all in a critical condition, had been dressing for a Christmas party when the explosion occurred.
Anya Evans, 15, her sister Kira, 14, and their friends Nadine Fardon, 14, and Kimberly Patterson, 15, ran screaming into the street with their clothes on fire.
Neighbours came to their aid and the four were taken to hospital. They suffered up to 40 per cent burns and will need skin grafts, doctors said.
Twenty-five firemen were sent to tackle the blaze in Llanelli, South Wales, on Monday.
The girls' parents were too upset to talk. But they released a joint statement thanking the emergency services and the hospital, and the residents who helped their daughters.
They added: "We are totally devastated by what has happened and are praying for the girls' recovery."
The Evans sisters had invited their two friends to their home to dress. It is not known which brand of tongs they were using.
There are several popular models which are powered by refillable gas canisters.
These provide a portable source of heat for curling or straightening hair.
Police and fire crews are sifting through the gutted bedroom for clues to why this particular gadget blew up, but it will be several days before they can interview any of the girls.
The explosion could be heard for miles around, and neighbours on either side were forced to evacuate as the flames spread onto their roofs.Nicola Paskin, 34, said: "The girls were seen fighting their way through smoke and flames to get out of the burning house.
"They looked very distressed and their clothes were blackened.
"The trouser legs of two of them were burned right off and one of the others had cuts to the face."
The girls were being treated in the specialist intensive burns unit of Swansea's Morriston Hospital after suffering between 29 per cent and 41 per cent burns.
Hamish Laing, consultant plastic surgeon at the unit, said: "They suffered burns to their faces and have already undergone surgery.
"It was a flash flame injury in a confined space. But we won't know exactly what happened until the girls wake up and tell us.
"Their condition is critical and they are on breathing machines.
"But we are optimistic about their condition - their injuries are hopefully not life-threatening and we believe they will get better."
He added: "All four girls will need skin grafts and at least one will need plastic surgery.
"All four are critically ill and we expect that to be the case for several days."
The girls were pupils at Coedcae Comprehensive in Llanelli, South Wales.
Headmaster Harvey Jones said: "We are deeply saddened to hear of the injuries suffered by the girls.
"They are very lively characters with a large circle of friends within the school.
"We are in a state of shock at the fire and have held a special assembly to share our feelings."
Town councillor John Jenkins said: "Looking at the state of the building it is amazing that anyone got out alive. It's a Christmas miracle that the girls survived."