Southern train services were halted after a freight train jumped off the track in Ratchaburi province on Monday.
The State Railway of Thailand said all southern train services were affected. Workers were on the scene to clear the track. The freight train derailed between Ban Ku Bua and Ratchaburi stations.
The derailment blocked trains to and from the southern region.
Trains out of Hua Lamphong were waiting for clearance at several stations before Ratchaburi station. Express train No 40 from Surat Thani to Bangkok stopped at Phetchaburi station and transferred passengers to Bangkok and other destinations by bus.
The cause of the derailment was not known.