POLICE are hunting two youths seen riding the back of a train in behaviour described by rail chiefs as deplorable.

The risky riders were photographed at Jolimont station in Melbourne about 4pm on Saturday.

A witness who provided the photo to the Herald Sun - who asked not to be named - said he had just travelled with friends to the station.

"I'd just got off that train. I was hanging around on the platform talking for a moment when I noticed there were a couple of people who'd hopped on the back of it," the witness said.

"One of them put his hand over his face so he couldn't be seen in my photo."

Melbourne's rail service Metro will hand over CCTV footage taken at the station to identify the two.

Another passenger contacted Metro on the platform emergency intercom, then then saw the Eltham-bound train depart.

"A friend of mine was actually at Clifton Hill station half an hour later, and he happened to notice a couple of people hanging off the back of a train," the witness said.

Metro spokeswoman Geraldine Mitchell said the pair's behaviour was deplorable.

"This pair risked their lives through this stupid, dangerous and irresponsible behaviour," Ms Mitchell said.

Express trains between Jolimont and Clifton Hill can reach up to 70km/h.

Train services along the Epping and Hurstbridge lines were delayed after drivers were alerted.

Victoria Police spokesman Adam West said the incident was being investigated, and anyone who can identify the people in the photo is urged to contact police.

Originally published as Train passengers snap riskiest of rides