A large hole has opened up above one of the tunnels built for the HS2 high speed rail line.
A spokesperson for HS2 Ltd said that the hole near Little Missenden, Buckinghamshire, was above part of the Chiltern tunnel and that the company had notified the Environment Agency and were engaging with the landowner.
They added that investigations were ongoing but that the opening was probably linked to “pre-existing ground conditions”.
Campaigners against HS2 have said that the hole, which they have measured as being about six metres in diameter and five metres deep, showed that it was “time to stop digging”.
The 16-kilometre Chiltern tunnel is the longest on the HS2 project. HS2 Ltd said the site had been sealed off and “there is no risk to the public”.
For the past 21 months, tunnelling machines have been working to excavate the high-speed rail project’s route under the Chilterns in Buckinghamshire.
The two tunnels, between the M25 and South Heath, have five shafts for emergency access or ventilation near Chalfont St Peter, Chalfont St Giles, Amersham, Little Missenden and Chesham Road and form part of the first phase of the route between London and the West Midlands, which is expected to begin operating between 2029 and 2033.
The route will eventually link back to Manchester.
Last month, the chief executive of one of HS2’s biggest contractors said that the project needed a “major rethink”.
Bob Pragada, head of the Fortune 500 engineering consultancy Jacobs, suggested Boris Johnson had failed to scrutinise data on travelling patterns and demand properly before he greenlit the controversial project.
He said that it was time to pause and properly analyse this data before deciding which parts of the project should be prioritised.
The call for more detailed analysis came after Mark Harper, the Transport Secretary, announced last month that HS2 would be pared back and delayed to combat its soaring costs.
A DfT spokesman said at the time: “HS2 continues to represent a crucial investment into our national infrastructure, levelling up communities right across our country, providing a net-zero alternative to car travel and domestic flights, increasing capacity on our rail network and training a skilled workforce for the UK’s future construction industry.”