There was one slippery customer on board a train south of Sydney overnight.

Passengers on the 6.54pm service from Kiama to Central on Tuesday were stunned to find they were sharing their carriage with a small snake that was slithering along the overhead luggage rack.

Stunned passengers found the snake on the South Coast Line train. Credit:NSW TrainLink

A NSW TrainLink spokesman said passengers on the South Coast Line service alerted staff as the train approached Wollongong station.

All passengers were moved off the carriage, which was locked for the rest of the journey to Sydney.