There are fears that the redevelopment of a Norwich hospital could cause nearby homes to subside - or even collapse - into underground chalk tunnels.
Health bosses have lodged plans for a £9m revamp of the Norwich Community Hospital site, off Bowthorpe Road, in the west of the city.
The existing building would be knocked down and replaced with a five-storey hospital, alongside a new care home, care units and worker accommodation.
But people living on Merton Road, to the east of the site, say they have 'major concerns' about how the ground beneath their homes could be affected.
Archeologist and university lecturer Dr Joanne Clarke claims many properties in the area sit above unmapped and unstable chalk tunnels - and she believes vibrations from work on the development could cause a collapse.
Dr Clarke said: 'Leaving aside a major collapse of someone's house, the most obvious issue is that subsidence could cause cracks to appear on people's homes. The [hospital] car park has never been built on because of this issue and it is known the ground is unstable.'
She added that her own home sits above a 60ft void, but was built on top of 18 metres of piling to ensure it does not fall in.
Dr Clarke said the tunnel under her house leads in the direction of the hospital car park.
Outline plans for the site's redevelopment, lodged with Norwich City Council, show a new multi-storey care home planned for the car park area.
A Norfolk Community Health and Care NHS Trust spokeswoman said: 'The project is currently at submission for approval stage and the outline application approval submission documents are available online. We are very conscious of the concerns of neighbours on this matter and we are sharing information at all stages of the project.'
She said an outline business case was being prepared for October and would involve further survey work, which will establish site issues and ground risks, including that of any potential subsidence in the surrounding area.
Claire Stephenson, 43, of Merton Road, said the 'destabilising' of land was her biggest worry.
Meanwhile, resident David Kent added: 'We support the NHS improving hospital facilities on this site.
'However, we are concerned that the developers have not fully considered the historic instability of land in this area.'
Subsidence in Norwich has produced devastating consequences over the years, not least on May 11, 1936, when an 80ft-deep sinkhole swallowed three homes on Merton Road.
The disaster, eight decades ago, claimed the lives of Thomas Hall and his wife, whose immediate neighbours were Russell and Rosa Goodson.
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