Two passengers were killed late Thursday night when an air-conditioned Bangkok-bound bus from Tak plunged into the drainage ditch between carriageways in Nakhon Sawan.
The driver and 36 other passengers were injured, with five left in serious condition.
Police said the accident occurred on Phaholyothin Road at Ban Thanon Khong, Tambon Nong Krod, Muang Nakhon Sawan.
Two women – Nini Aung, 32, from Myanmar and Pimlapha Kwinwalai, 24 – were killed when they were thrown from the bus.
Driver Suriyan Soomlai, 36, told police a motorcycle cut in front of him and he lost control in attempting to avoid a collision.