“Thankfully no one died,” BTP tweeted shortly after 9:00 p.m. (5:00 p.m. EDT) local time on Sunday.
The agency said officials were continuing to respond to the incident in the Fisherton Tunnel.
Earlier on Sunday, BTP officials were called to aid, “following reports of a train derailment.”
A tweet by Wiltshire Police also said police officers were responding with a fire and ambulance service “at the scene of a train accident involving two trains between Andover and Salisbury.”
A statement from Network Rail Wessex said the incident involved a Great Western Railway service between Portsmouth Harbor and Bristol Temple Meads at 17:08 and a South Western Railway service from London Waterloo to Honiton at 17:20.
Network Rail Wessex said emergency services do their job, so the line remains closed.
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