Updated 11.47am: Auckland police say the man hit by a freight train early this morning was walking along the tracks towards the Papatoetoe railway station when he was hit.

The 59-year-old was hit just after 6.30am.

South Auckland rail commuters will have their journeys considerably delayed this morning for some time while police clear the scene - the southern line is blocked from Otahuhu to Homai, and travellers should use buses.

A rail shuttle is operating north to Homai and south to Otahuhu.

Northern Communications Shift Commander Inspector Tony Wakelin says this has been a traumatic experience for the train driver and Victim Support has been arranged.

KiwiRail says it's a tragic reminder for people to stay off railway tracks.