At least 30 passengers, mostly foreign tourists, are reported to have been injured when a train derailed in the mountains of northern Thailand.

It was the second derailment on the same route in a month.

State Railway of Thailand governor Prapas Jongsanguan said the overnight train from Bangkok to Chiang Mai skidded off the tracks early today (Wednesday) in Phrae province.

Seven out of 10 carriages flipped on to their sides.

Railway authorities believe the accident was caused by old tracks that were scheduled for repair.

Prapas said one passenger was seriously injured. The rest suffered minor injuries and were provided free transport to their destinations.

Another Bangkok-bound train from Chiang Mai derailed early this month but no one was injured.

The Bangkok-Chiang Mai train is popular among foreign tourists.