A large hole has opened up above one of the tunnels being built for the high speed HS2 railway line.
Anti-HS2 campaigners said the hole in Little Missenden, Buckinghamshire, was evidence that tunnelling on the controversial infrastructure project should stop.
But a HS2 spokesperson said the hole, around four metres across, was likely related to “pre-existing ground conditions”.
The spokesperson said the hole, said to be around three or four metres deep, had opened up above part of the Chiltern tunnel and that the company had notified the Environment Agency.
“We are aware of a small area of ground movement within a field above the Chiltern tunnels,” he said.
“Investigations are ongoing, but this is likely to be linked to pre-existing ground conditions above the tunnels. The site has been sealed off and there is no risk to the public.”
The Chiltern Tunnel is the longest tunnel on the HS2 route between London and Crewe at ten miles long and will carry passengers under the Chiltern Hills.
Two 2,000 tonne boring machines launched in the summer of 2021 and are around half way through creating the tunnel.
The twin-bore 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.
It is part of the first phase of works for HS2 which is expected to be operational between London and Crewe between 2029 and 2033.
The route will eventually also link to Manchester.
It comes after the Government earlier this year announced pared back plans for the railway because of soaring inflation.
Ministers said they had “switched priority” to get the high-speed railway running from Birmingham to Old Oak Common, deferring construction of a 7.2km tunnel between Euston and Old Oak Common stations.
A HS2 spokesperson said at the time: “The two Tunnel Boring Machines (TBMs) building the tunnel on this section from the Old Oak Common Box towards Euston were scheduled to begin in 2024, but this is now deferred.
“The preparation works for the launch of the two TBMs will continue.”
In January, Chancellor Jeremy Hunt said he does not see “any conceivable circumstances” in which the High Speed 2 rail line would not run to its planned Euston terminal.