Ulykken skete ved midnatstid natten til fredag i Lom Sak-distriktet i provinsen Phetchabun, da bussen var på vej til den nordlige provins Chiang Rai.
»Vi formoder, at chaufføren faldt i søvn,« siger politichef Sukit Samana til AFP.
»Vi fandt 28 lig ved ulykkesstedet i kløften, der er 30 meter dyb, og en mistede efterfølgende livet på hospitalet,« tilføjer han.
Fire andre er indlagt i kritisk tilstand.
Øjenvidner har fortalt, at bussen kørte meget stærkt, før den kørte af vejen.
Bussen, der havde 40 passagerer om bord, blev fuldstændig ødelagt.
At least 32 killed when bus falls from bridge into 50-metre ravine in Phetchabun
At least 32 people were killed when a bus from Khon Kaen heading to Chiang Rai fell from a bridge and plunged into a 50-metre ravine in Phetchabun late Thursday night, police and the transport minister said.
Pol Lt Col Surawit Chaisit of Banklang police station said the bus crashed into the guard rail of the Khun Pha Muang bridge, which is the bridge with the tallest supporting pillars in Thailand, and fell down.
He said the bus was carrying 40 people. He said 27 bodies were found in the bus and many more outside. So far, rescue workers retrieved 31 bodies were still searching the area.
Five severely injured were rushed to two hospitals and one of them died at a hospital.
Transport Minister Chadchart Sittipunt said in his Tweet message that the accident happened at 11 pm.
The Nation
He said the bus was carrying 40 people. He said 27 bodies were found in the bus and many more outside. So far, rescue workers retrieved 31 bodies were still searching the area.
Five severely injured were rushed to two hospitals and one of them died at a hospital.
Transport Minister Chadchart Sittipunt said in his Tweet message that the accident happened at 11 pm.
The Nation