Three schoolgirls died aged 10 to 12 while cooling off in a river amid a heat wave in Thailand.

The youngsters took a dip in the Sai Buri River as scorching temperatures reaching 40 degrees Celsius baked Pattani province on April 24 afternoon.

However, one of the girls, Nurahuda, began to drown when she wandered off into a deeper part of the river.

Her friends managed to save her, but they also drifted away from the riverbank and struggled to stay afloat.

Passing villagers who later saw them flailing in the river rushed to their aid and called local rescuers.

Only Nurahuda was reported to have survived. Her friends, Peeyana, 10, Maimoon, 12, and Nurhasima, 11 - all residents of the neighbouring Ban Plak Taen village - had drowned.

A rescue officer said: 'At around 3 pm, the rescue team Sawang Saiburi received a report from the head office about the girls drowning in the river.

'By the time we arrived at the scene, one girl had already been pulled ashore by villagers. We performed first aid, but she was not breathing and saliva was foaming out of her mouth. Our rescue team then proceeded searching the rest of the girls' bodies.

'As far as we know, the four girls went to the river together. The water is not that deep, but the girls are small, and the area they were swimming in had a hole or groove underwater which was dug out by a tractor. The water there was around two metres deep.

'The sole survivor was the first to drown. The others noticed and went to help her. She may have grabbed her friends and, in struggling to pull herself up, dragged them down and probably caused them to drown.

'The survivor was saved by group of villagers around there first, then we were called to help the other girls.'

Authorities said the incident was being investigated.