The accident took place a little past midnight at a spot between markers 673 and 674 on the Phaholyothin highway, in tambon Na Saeng, Koh Kha district.&nbsp; 
The two injured staffers were sent to a local hospital.&nbsp; 
Most of those who escaped unharmed could not tell police how the accident had happened as they were asleep. 
Pol Captain Sirawit Chaiyawan of the Koh Kha Police Station said police suspected the crash was either caused by the bus skidding on the slippery road following rains while going downhill or by the bus driver dozing off behind the wheel.

Two injured as bus crashes into tree in Lampang

Two people were seriously injured when a bus transporting some 40 employees of the Electricity Generating Authority of Thailand (Egat) after a field trip to Chanthaburi province, lost control and crashed into a roadside tree in Lampang province early on Sunday.