The fire was discovered by the driver, who saw smoke coming from an air-conditioning unit above the guard's compartment.

The train was on the Eastern Suburbs and Illawarra line heading to the city near Wolli Creek station just before 8am yesterday, NSW Fire Brigades' Craig Brierley said.

He said about 1000 people were evacuated from the train and asked to change trains at Wolli Creek station.

Those passengers at Arncliffe and Banksia were advised to join another service to get into the city.

The worst affected was an interurban service from Kiama to the city with delays of about 35 minutes.

No one was injured in the blaze.

The fire was extinguished by 8.30am and the train was towed to a workshop.

Two weeks ago commuters on the same train line were left stranded in peak hour after power lines were damaged at Tempe station.

On that occasion commuters faced delays of more than an hour during the morning peak.

The Opposition's transport spokeswoman, Gladys Berejiklian, expressed concern at the frequency of train breakdowns following this morning's incident.

``Unreliable services are a daily issue for commuters,'' Ms Berejiklian said. ``Today's breakdown is not an isolated incident, in fact over the past 11 days there have been 23 train breakdowns due to maintenance failures.''