A man has died while train surfing in Brisbane's south, with police saying CCTV footage showed he had been spraying graffiti.

Queensland Police say the incident occurred about 1.30pm (AEST) on Thursday at Runcorn on the Beenleigh line.

"CCTV footage shows a man train surfing and graffitiing a train," a police spokesman said.

"The man has fallen off the train and died."

A second train travelling in the other direction stopped when the driver spotted the man on the tracks but it is understood he was already dead.

The spokesman said emergency crews were on the scene and investigations were continuing.

Inspector Tim Peters said it was a reminder to act responsibly around trains.

"The railway is not a playground," he said.

"People should not put themselves at risk around trains."

A Queensland Rail (QR) spokeswoman said their own response units were also attending the station.

"We are working with police to investigate the incident and we are unable to speculate on the circumstances," the spokeswoman said in a statement.

The investigation caused major delays on the Beenleigh line and buses were taking commuters between Banoon and Kuraby stations on Thursday afternoon.

Train services have resumed but at 5.30pm there were delays of up to 30 minutes on the Beenleigh and Gold Coast lines.

ABC/AAP