The local police said they received the distress call around 2 am.
At the site of the accident, in Nakorn Thai District, police discovered that an unroofed red two-storey bus has plunged off the moutainous highway and landed 50 meter deep in a nearby gorge.
The bus was operated by Chakrapongse Tour Company. The wounded were rushed to Somdej Yuparart Nakorn Thai Hospital and Somdej Yuparart Darn Sai Hospital.
The accident killed 5 victims, including a 7 month-old toddler. Some of the wounded are reported to be in critical condition, including Ms. Magdalena Jaworska, a 30 year-old foreigner in her 4th month of pregnancy.
The bus was carrying passengers at its full capacity from Udorn Thani to Chiang Mai, police said. The bus reportedly suffered brake failure and crashed into a van on the descent section of the highway before plunged down into the gorge. However, police said additional investigation was underway for a clearer picture of the accident.
A passenger on the bus, Mr. Chokechai Yachara, 46, said a burning smell was noticed as the bus entered Loey province and the bus driver stopped to inspect the problem at a local ranger checkpoint. The bus nonetheless continued its journey and the driver appeared to be struggling with the brake moments before the accident, according to Mr. Chokechai.
Later, Mr. Nattapon Lertmongkol, 24, identified himself to the police as the driver of the van. Mr. Nattapon told the police he was descending down the highway when a the bus hit his van from behind, then plunged off the highway. He said a passenger in his van was slightly wounded by the accident.