A fire broke out in the booking office of Gloucester railway station in the early hours if Friday.
Crews were called to the two-storey building on Bruton Way just before 0130 GMT. The ground floor was severely damaged.
A 17-year-old male from Cheltenham has been arrested on suspicion of arson.
The station was closed during the incident but partially reopened later, the fire service said.
Passengers were advised to check their journey before travelling.