Southern Line is a metre-gauge railway line in Thailand, owned by State Railway of Thailand (SRT), which runs through most of the provinces in the Central, Western, and Southern regions of Thailand. At 1,144.29 kilometres in length, it is Thailand's longest railway line. It consists of the which stretches from Bangkok Hua Lamphong to Su-ngai Kolok District, Narathiwat Province, in the far south of Thailand, 1,140 kilometres from Bangkok. There are seven branch lines off this main line: