A service update on the LNER website has a 'do not travel' warning although no official statement has been made.
Rail industry insiders say that all 65 of the Hitachi-manufactured Azuma trains are being investigated for potential cracks on their chassises after Great Western Railway, who also operate the model, discovered the defect during routine maintenance.
Freelance rail journalist Philip Haigh also suggested that a newly-found fault may also be to blame.
"The first cracks were found in Hitachi trains a few weeks ago. So was today’s mass withdrawal pre-planned or an emergency measure decided overnight? Lack of warning suggests emergency but problem is weeks old so surely time to plan?
"Sources suggesting that it’s not the cracks found weeks ago that are the problem. Hitachi is now looking at the attachment of lifting jack pockets to the bodyshells. Likely to be more of a problem in older fleets, ie more GWR than LNER, TPE or Hull."
All of the Azuma units - which make up the entire LNER fleet since the old InterCity 125 and 225 units were phased out - will require inspection and possibly remedial work before they can return to service.
LNER said on Twitter: "We are only running Azuma trains at the moment and these are currently being checked. Once we have more information, this will be made available to all."
"Due to a problem under investigation, services route wide are subject to delays and cancellations. Please DO NOT TRAVEL, tickets will be valid up to and including Sunday 16 May 2021 (a new reservation MUST be made)."
Hull Trains confirmed that the problem was also affecting their own Hitachi Class 800 trains, which have also been 'grounded'.
Transpennine Express's Nova 1 trains are being inspected and there is consequently severe disruption on their Liverpool to Newcastle route, which serves Huddersfield, Dewsbury, Leeds, Selby, York, Hull, Malton, Scarborough, Thirsk and Northallerton.
"A number of Class 800 series Hitachi trains from several train companies have been taken out of service today for checks as a precautionary measure. This problem is being investigated by Hitachi and once trains have been checked, we hope to be able to release them back into service."
"A number of Class 800 series trains from several train companies have been taken out of service today for checks as a precautionary measure, including our Nova 1 trains.
"This problem is being investigated by the train manufacturer and once trains have been checked, we hope to be able to release them back into service as soon as possible.
"This will affect a significant number of services on our Newcastle to Liverpool route and we are advising customers not to travel on this route today."
Trade union the RMT also issued a statement in which they highlighted safety concerns: "RMT is fully aware of the issues that have led to the cancellation of services on LNER today and that similar problems with cracks appearing in the fleet on Great Western are also emerging.
"Hitachi needs to ensure the highest safety standards and properly investigate and rectify the issues.
"This situation demonstrates once again that it is reckless for the rail companies and the DfT to move the industry to diluted, risk-based maintenance regimes which extends maintenance cycles on rolling stock or on the infrastructure, whether that be on the mainline railway or on the tube and metro services, to cut costs and strip out staff.
"The railway needs to be maintained rigorously and to the highest possible standards to protect the travelling public and the staff and that will remain RMT's key demand."
In November 2019, an Azuma which had only been manufactured a few months previously suffered severe damage in a crash with an older High Speed Train while both were approaching the Neville Hill depot in Leeds.
The cause of the collision was found to be due to the Azuma's driver misunderstanding its on-board software on his third time at the controls and unintentionally accelerating.
The Rail Accident Investigation Board found the Azuma driver had been unable to set up the train management system because 'ambiguous documentation' from manufacturer Hitachi led to LNER 'misunderstanding the required process' when it developed its driving training programme.
The Azumas have only been in service on the East Coast Main Line for two years, arriving in May 2019.