One service was heading to Honiton
Investigations are underway in to what caused two trains - one heading to Honiton from London Waterloo - to crash near Sailsbury.
The 1720 South West Railways service collided with a GWR train running from Portsmouth Harbour to Bristol Temple Meads on Sunday evening.
The GWR train hit an object in a tunnel at around 6.45 p.m., causing part of it to come off the tracks. That knocked out local signalling, and the Honiton service hit it shortly after.
Seventeen people were treated in hospital, including one of the drivers who had been trapped in his cab in the Fisherton Tunnel.
The westcountry-bound train would normally have continued onto Exeter, but engineering works at the weekend meant it should have terminated at Honiton.
Passenger Angela Mattingley said there was some panic when everything went black. Lucy Gregory said she was thrown across a table by the impact and ended up on the floor. "They smashed the windows and we got out of the window. It was really scary," she told reporters.
Trains are not running through the tunnel today whilst investigators continue their work.