Eyewitnesses said some of the teachers were thrown as far as 20 metres away from the site of the accident, while other had drown in the river or went unconscious after falling into the water.

The accident occurred at about 9.30am on the Chiang MaiChiang Rai highway in Tambon Pa Miang, about 30 kilometres from Chiang Mai City.

The doubledecker lost control at a sharp curve near a bridge over Kuang River, overturned and plunged into the river, police said. The injured were evacuated on helicopters to nearby hospitals.

The bus was hired to take teachers from eight schools in Chan Thaburi's Pong Nam Ron district for a fieldtrip in Chiang Rai.

The bus left Chiang Rai at 7 am for a tour on Doi Inthanon and the Royal Flora Ratchaphruek 2006 Exposition, respectively.

A Klong Bon Wittayalai School teacher, Amnat Chayangkhanont, who sustained head injuries, said that the bus driver was speeding and lost control at a curve and then plunged into the river.

At the time of the interview, Amnat still didn't have an idea over the fate of his wife or her whereabouts.

Meanwhile, Chanthaburi Educational Zone 2 Director Somchai Jitneuang said that he had contacted Chiang Mai Educational Zone 1 Director to assist the victims.

Somchai said he would provide assistance to the injured and the dead as according to the civil service procedure because the group had obtained a fieldtrip permit to learn teaching methods in the North and to visit the horticultural expo.