Some Sydney train services were delayed by up to an hour because of urgent overhead wiring work at Wynyard in the city's CBD.
People in Sydney on Saturday were urged to avoid travelling on trains, because of cancellations and major delays due to urgent repair work.
Sydney Trains tweeted that due to a technical issue affecting the service's communications indicator boards, real time apps and train running information may be unavailable or incorrect.
It earlier said that there was urgent overhead wiring repairs being done at Wynyard in the city's CBD, and that services between Wynyard and Central were suspended in both directions,
It also tweeted that and other services may be cancelled, terminated early or otherwise modified at short notice.
Some commuters tweeted that their trains had been delayed by up to an hour, and there were also reports of people getting on the wrong trains because of the incorrect information available.
NSW Labor has called on Sydney Trains and NSW Transport Minister Andrew Constance to assure commuters that trains will be running to normal timetable by this afternoon with major sporting events taking place.