At least 17 schoolgirls have died after a fire swept through a dormitory at a school for girls from poor hill-tribe families in Thailand.

Police said a further five girls were injured in the blaze.

The fire broke out late yesterday as the girls, aged five to 12, slept at the Christian Pitakiatwittaya School in the northern province of Chiang Rai.

A local police spokesman said: "Most of the losses were because the children were asleep."

He added that two of the injured were in critical condition.

Forensic experts sifted through the debris and ashes inside the concrete shell of the school dormitory building in an attempt to identify the source of the fire.

Preliminary indications suggested a faulty fluorescent light on the ground floor may have been the cause, a senior regional forensics officer said.

A hot fragment fell onto a pile of clothes and started the fire, he said, adding that the children likely died due to smoke inhalation.

"There was a lot of smoke and the room where it happened was right below where the children were sleeping," he said.

A total of 36 children of the 142 that attend the school were in the dormitory when the fire started, the head of the school said.

She said the alarm was raised by a school cleaner.

"I am at a loss for words," she said. "I don't know what I should do, but the only thing on my mind now is to try to find a way to ease the parents' suffering."