Plans for a futuristic "hover train" that could get passengers from Liverpool to Manchester in just seven minutes have been submitted to transport bosses.
Direct City Networks (DCN) is developing a plan for "the world's fastest underground system".
But the plans have been discounted as "laughable" by a leading industry expert.
Transport for the North (TfN) said the plans needed more "development".
The Liverpool Echo reported how the DCN300+ would be a Maglev - magnetic levitation - system in which vehicles hover above tracks and are propelled by electrically-charged magnets.
That reduces friction to a minimum and means vehicles might go at up to 350mph - faster than any conventional train in Europe.
But Tony Miles, who writes for Modern Railways, said the plans were not based in real science.
He told the BBC: "I have seen similar things being discussed over the last year from what I would call the mad scientists.
"What they don't work out is the fact that accelerating to that speed and then braking again would probably vaporise the people inside the train.
"I think serious scientists would fall about laughing at it."
The DCN plan would see Maglev trains put into a tunnel stretching across the north of England. Its initial plans suggest the journey from Liverpool to Hull could take just 29 minutes.
A line between Manchester and Leeds is said to have a journey time of nine minutes.
Rather than using long "trains", the system would instead use passenger pods, or capsules. The plans could cost over £3bn.
Development work needed
A TfN spokesperson said: "TfN have been provided with information by Direct City Networks (DCN) PLC regarding a proposal to initially link Manchester and Leeds with a high speed 'MagLev' connection, with the possibility of this being extended to Liverpool and Hull.
"We have responded to DCN highlighting several areas where we think substantive additional development work would be needed before any proposal could be given more detailed consideration."
In 2015, a Maglev train in Japan set a world speed record of 373mph on a test track.
DCN could not be contacted for comment.