Sydney Trains employee hit and killed by a train while working on the tracks

A rail maintenance employee has been struck and killed by a moving train while working on the tracks in Sydney's west.

Sydney Trains said the employee was carrying out "important maintenance work" on the tracks between Clyde and Auburn stations this morning when he was hit just after 6am by a Sydney-bound service from the Blue Mountains. 

An investigation is now underway into the incident.

"I am shocked and saddened by this news and I know that Sydney Trains and NSW TrainLink will work tirelessly with the relevant agencies during the investigation," Transport Minister Andrew Constance said.

Sydney Trains CEO Howard Collins said support was being offered to the employee's family. 

"Sydney Trains is working with the authorities at the scene to determine the cause of this incident," Mr Collins said. 

"The safety of our workers is our top priority and will be fully investigated by the relevant independent authorities."