Story highlights The dormitory house girls aged between 5 and 12 years old

Thai investigators are trying to confirm the cause of the blaze

Bangkok (CNN) Parents rushed to an elementary school in Thailand Monday, where 18 girls were killed overnight in a fire at their school dormitory.

"It is still very chaotic here," the school's manager Rewat Wassana told CNN. "We are in the process of identifying bodies, none of the parents can claim their children's bodies yet," he said.

Bodies lie on trolleys awaiting identification after the Sunday night blaze.

Thirty-eight children -- all girls between the ages of 5 and 12 -- were sleeping in the dorm when the fire broke out at the private Pitakiatwittaya School Christian elementary school in Thailand's northern Chiang Rai Province, according to lead investigator, Police Captain Kachornsak Pongthit.

It's not clear what caused the fire, which is believed to have started around 11:00 p.m. local time Sunday (12 midnight Saturday ET).

The blaze started at about 11 p.m. local time Sunday night while the girls were sleeping.

Twenty girls were rescued after firefighters on ladders scaled the walls of the building, said Sawang Momdee, chief of Chiang Rai's fire unit, who led the operation. Of the 20 rescued, five were injured.

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