The south-bound train struck the three-metre-long piece of unused rail shortly after 2pm, within 500 metres of the Longford bridge.

The piece of metal was propped up on the track at a 45-degree angle, facing the oncoming train.

The train was unable to stop in time and hit the piece of rail.

TasRail chief executive Damien White said the rail deflected off the train's front guard, but might have pierced the cabin or gone under the train and pierced the fuel tank.

Mr White said not only did the attempted sabotage cause significant delays, but the train might have exploded if the tank had been pierced, causing serious injury and/or death.

"The two drivers on board were shaken, but luckily unharmed," he said.

"Last week saw a multimillion-dollar ballast regulator, newly arrived from the US, shot at, with the cabin window pierced 5 millimetres into a 15-millimetre bulletproof glass on the West Coast.

"This recent spate of potentially deadly incidents are unnerving for our people."

Incidents in the past few weeks include youths jumping off rail bridges in front of oncoming trains at Longford, Deloraine and Heybridge, and a man dashing across a rail line at Burnie, with children in tow, giving the oncoming train "the finger".

Mr White said such behaviour did not reflect the broader community, but it painted a "disgraceful picture".

He urged the public to come forward with information.

"We are appealing to all Tasmanians to help us, before someone gets killed," Mr White said.

Police examined the Longford scene yesterday and are investigating the recent incidents.

Witnesses can call Crime Stoppers on 1800333000.

Email: ctang@examiner.com.au