Around 300 passengers were reportedly made to walk down a railway track in the dark after the new high-speed train they were travelling on broke down.
Commuters on the Penzance to London Intercity Express service had to wait for more than six and a half hours for their train to be evacuated before boarding a rescue service back to Exeter.
Other services also faced disruption, with some journeys delayed by more than three hours.
Customers documented their experiences on social media.
Nurse Greg Dix was travelling to London for a conference and arrived at his hotel in the city 12 hours after departing from the West Country.
Not all customers were satisfied with the company's rescue efforts and complained on social media.
Katharine McMahon's daughter was stranded on the broken down train near Tiverton for more than five hours.
Great Western Rail are offering full refunds and a free journey for customers affected.