The incident occurred around 9 a.m. when the engine of Metrolink train 811 caught fire after it had departed from the Tustin train station, said Metrolink spokesman Scott Johnson.
All crew members and the 54 passengers aboard the train were safely removed. No injuries were reported.
Orange County Fire Authority firefighters responded to the blaze and extinguished the flames, Johnson said.
All train traffic in the area was stopped for an undetermined amount of time, he said.