A 20-metre section of a controversial new Tesco store at Gerrards Cross in Buckinghamshire fell in at about 7.15pm, sending hundreds of tons of rubble on to the tracks. Minutes earlier a crowded passenger train stopped outside the tunnel after its driver noticed debris falling from the tunnel roof, witnesses said.
Brett Jackson described hearing a sound "like an earthquake" as the tunnel caved in. He told BBC News 24: "It still looks very unsafe, as if the rest of it could collapse at any second."
The £20m Tesco project – which involves covering a 150-metre section of the line and building the store on top – has been the subject of local protests. Residents of the prosperous commuter town who opposed the plans have vowed to boycott the new store. Tesco withdrew plans for a larger store after a poll of 8,600 residents, including Cilla Black and Ozzy and Sharon Osbourne, found 93 per cent against it.
Construction work, which began several months ago, has only been possible after 1am while trains are not running.
Chiltern Railways, which operates services on the line, said initial assessment suggested it would be blocked for at least two days and replacement bus services would take commuters into London.
British Transport Police said: "Reports are that a large section of the construction collapsed on to the railway line below. Consequently a large amount of debris blocked the line. Luckily no trains were passing underneath at the time.
"A train was stationary at Gerrards Cross station at the time of the collapse and the driver witnessed the incident. As a result he quickly advised his control and trains were stopped. One train with about 70 passengers on board was stranded for about 15 minutes but was taken back to the nearest station at Denham Golf Club.
"At the time of the incident no work was being carried out at the site and there are no reported casualties."
A Tesco spokeswoman said: "A section of rail tunnel at our new Gerrards Cross site has collapsed. Thankfully we understand that no one has been hurt but rail services are obviously disrupted, for which we apologise. We have launched an urgent investigation with our engineer contractors and will work with the authorities to understand what happened and get rail services back to normal as soon as possible."Reuse content