Two brazen teenagers have managed to persuade heritage rail volunteers to let them drive a train from a workshop in southeast Queensland.

But the would-be train thieves were only able to drive the diesel locomotive about a metre before crashing it into carriages and raising suspicions.

Mary Valley Heritage Railway (MVHR) President Tony Hallam says a man entered the group's Gympie workshop on Tuesday pretending he was "a person of authority" and a qualified train driver.

His claims were backed by one of the organisation's volunteers who accompanied him.

But Mr Hallam said another volunteer realised the man wasn't who he said he was, when he clearly couldn't operate the train's braking system.

"The heritage diesel locomotive actually bumped three heritage carriages onto a heritage rail motor," he told AAP.

Mr Hallam said a volunteer contacted him after the crash.

He then confronted the man and, after he was unable to produce any credentials, contacted police.

Mr Hallam said he was shocked at the teenagers' audacity, particularly given the potential dangers of their actions.

"This individual may have got it into his head to head onto QR (Queensland Rail) tracks," he said.

"The scenarios are frightening and fortunately the MVHR volunteer from the shed here realised something was amiss and had the presence of mind to contact me."

There did not appear to be any significant damage, Mr Hallam said.

A 17-year-old, from Brisbane, has been charged with fraud, unlicensed driving and unlawful operation of a vehicle.

His 18-year-old accomplice, who volunteered at the organisation, has been charged with fraud.

Both will appear in Gympie Magistrates Court later in April.

The DH 45 diesel hydraulic locomotive in question was built in Maryborough in 1969 and was decommissioned in 2009.