From top left, clockwise: Kira, Anya, Nadine and Kimberly

Pupils at Coedcae School in Llanelli, Carmarthenshire, are also sending cards to the families of the girls.

Anya Evans, 15, her sister Kira, 14, and friends Kimberly Patterson, 15, and Nadine Fardon, 14, are at Swansea's Morriston Hospital.

Headteacher Harvey Jones said the whole school was "saddened and worried" about four girls he described as "lively".

Doctors believe at least one of the girls, and probably more, are likely to remain in hospital for some time and will need extensive surgery after Monday's blaze.

All four girls are on life support machines, with burns ranging from 41% to 29%.

Especially this time of year, the kids back in school are very saddened by what's gone on Harvey Jones, headteacher

Mr Jones said teachers and pupils were concerned about the girls and "keeping their fingers crossed".

"Especially this time of year, the kids back in school are very saddened by what's gone on. The youngsters [involved] were lively characters with lots of friends," he said.

"In order to give our youngsters a chance to get their heads round it we had some special assemblies where we talked about what had happened and remembered the kids in our thoughts.

"Those who know them are particularly saddened and worried."

The roof of the house was destroyed in the fire

He said some classes were sending cards to the girls' families and to the hospital.

An investigation has begun into how the blaze started.

There had been reports of an explosion before the roof of the mid-terraced house in Old Castle Road was engulfed in flames.

Fire investigators are examining the scene to discover the cause of the fire, which broke out at 1500 GMT.

Dyfed-Powys Police have already said it does not appear to be suspicious.