A roof of one of the houses was badly damaged

There were reports of an explosion before flames destroyed the roof of the mid-terraced house in Llanelli, Carmarthenshire at 1500 GMT.

Mid and West Wales fire service called it a "significant blaze", with some of the injuries involving up to 40% burns.

The girls, thought to be two sisters and two friends, aged 13 and 14, were taken to Morriston hospital, Swansea.

Road diversions were set up in Old Castle Road and people were asked to stay away.

The fire also caused some damage to two adjoining properties.

Andrew Francis, county commander for Mid and West Fire and Rescue Service, said he had been told by the ambulance service that some of the four teenagers, who were aged between 13 and 14-years-old, had quite serious burns, believed to be up to 40%.

The girls, thought to be two sisters and two of their friends, were out of the house by the time fire crews arrived.

A spokesman for the hospital said the girls were in a critical condition and it would give out more information on Tuesday.

We got up and rushed to the balcony and we could see the roof of the house collapsing Councillor John Jenkins

At least 25 firefighters from Llanelli, Tumble and Kidwelly were involved in the operation.

Dyfed-Powys Police said at this stage the fire, which was reported just after 1500 GMT, did not look suspicious.

An investigation is not expected to start until Tuesday morning.

The fire and rescue service earlier reported three mid-terrace properties "well alight", as it made efforts to stop the flames spreading to adjoining properties.

Local resident Malvern Evans said he could see smoke "billowing" from the houses affected.

"All the black smoke has stopped now but there is a lot of white smoke just coming up," he said.

"People passing the house have told us they saw some people getting into an ambulance and their clothes were all burnt and scorched."

He said the road had been closed to traffic and people had gathered nearby to see what was happening.

Local councillor John Jenkins said: "I was visiting a constituent's house, which overlooks the street, when we heard an explosion.

"We got up and rushed to the balcony and we could see the roof of the house collapsing.

"It was a miracle anyone survived that. The police have told me they think it was an aerosol or gas canister."

Meanwhile, Morriston hospital said on Monday evening its accident and emergency staff were "exceptionally busy" because of the incident, and appealed for people not to attend unless they had a genuine emergency.

I was just coming out of the leisure centre and all I could hear was sirens and as I was walking I saw flames coming out of the roof.
Louise, Llanelli

We saw the smoke at 3pm as we waited to collect our children from a nearby school and there was a lot of worry that some of the parents properties were involved. I feel so sorry for those involved to have lost so much this close to Christmas. I know that my family want to help in any way we can
Louise , Llanelli