A crumbling chalk mine has been discovered under the back garden of a house close to where a cave-in happened five years ago.
Homes had to be evacuated after a cave-in at Field Road
Engineers who found the mine in Reading, Berkshire, say "there is some cause for concern" and have told the residents not to go in the garden.
They discovered the shaft in Castle Hill while carrying out tests for mines in the Field Road and Coley area.
More than 30 homes had to be evacuated after a cave-in at Field Road in 2000.
Work to find any remaining Victorian mines was launched in May, with 700 residents in 285 houses asked to sign up for drilling tests.
The full extent of the mine found is still not yet known but no other residents have had to be warned of any danger so far.
A spokesman for Reading Borough Council said: "CCTV images of the mine galley have shown that it is deteriorating and that there is some cause for concern.
"The house-owners and occupiers of 127 Castle Hill, Coley, have been informed of the findings and advised not to use the back garden.
"They have also been given advice on potential dangers and precautions that can be taken."