Coventry’s "black hole" could keep the city’s High Street closed into next week – and beyond.

The street has been closed to traffic since the hole first appeared on Monday morning and three days on, experts are no nearer finding the reason for the sudden cavity.

Bomb damage has been ruled out while utility officials have failed to find anything that could have caused the hole, which is now growing as efforts are made to discover its cause.

Peter Chapman, head of highways and traffic management for the City Development Directorate, said: "Coventry Contract Services are excavating now and that digging has made the hole about four square metres.

"We are trying to find the cause of a the soft material. Normally an ingress of water, which erodes away the soft material, tends to cause these things but the ground underneath was quite dry.

"We have started to reach the services so we have had to tread carefully. Severn Trent Water and British Gas have been out and had a look at their apparatus and still we are not sure what has caused it.

"We have been asked if it could have been bomb damage but that area was not bombed, and we have not found any old cellars. The construction of the road has held up but obviously we need to find out just what has happened.

"We certainly don’t expect to be out of there in the next couple of days but won’t know that until we find the reasons behind it. It could possibly go into next week and we hope to know that in the next 48 hours or so."