BANGKOK (AFP): Four Malaysian tourists were killed and another 30 seriously injured in Thailand early today when their bus careened off the Asian Highway and overturned. The group was on its way to the southern city of Hat Yai, as part of a tour of Thailand that took them as far north as Chiang Rai. The accident occurred in Nakhon Si Thamarat province, 780 kilometers (485 miles) south of the Thai capital. Police said they believed the driver fell asleep at the wheel. Local police said the victims were one man and three women, all aged in their 30s or 40s, but officers were still trying to find their passports in order to establish identities. The tour company confirmed all the passengers aboard the bus were Malaysians, police said. It was the second horrific bus crash in just five days in Southern Thailand. On December 21, three people died and 36, including six tourists, were injured when a bus crashed in Phuket. Motorists in Thailand frequently complain of juvenile and arrogant road behavior from long-haul bus drivers, with many citing drug use as a major cause of bus accidents in the country.