Part of Chester's historical city walls has collapsed after digging work by developers.
Cheshire West and Chester Council said a section of the wall fell on Thursday evening, causing the development to be suspended.
"Early indications appear to show that earth was removed from the bottom of the city walls," a spokesman said.
Chester MP Chris Matheson claimed the developers had received safety warnings about digging so close to the wall.
Chester is the only city in Britain that retains the full circuit of its ancient defensive walls.
The city walls, parts of which are almost 2,000 years old, are the oldest, longest and most complete in Britain, according to Visit Cheshire.
Developer MJW Group was granted planning permission for new luxury apartments in the city in April.
"I am appalled that the company carrying out development on this site has not exercised the care and diligence that we expect to see in such close proximity to this iconic ancient monument," Mr Matheson said.
MJW Group has been contacted by the BBC for a comment.
The collapse took place behind Newgate Street near to the walkway leading from the Grosvenor Shopping Centre.
A council spokesman said: "A section of Chester's city walls collapsed last night after excavations being carried out by a private developer, working alongside the historic structure, compromised the integrity of the ancient monument.
"The removal of too much earth exposed a section of bare foundations."
Councillor Karen Shore, deputy leader and cabinet member for environment, highways and strategic transport, said the council was taking the collapse "very seriously" and would ensure a thorough investigation was carried out.
"I am thankful that no-one has been hurt as a result of this collapse and our priority will continue to be public safety," she said.
The collapse is close to the site of another collapse which happened almost 12 years ago.
A team of surveyors, engineers and archaeologists investigated after a 30m section of the wall came down in April 2008.
You may also be interested in:
- Chester's first fortifications date back to Roman times - about AD74 to 75
- Nothing is known about the walls' condition between the end of the Roman occupation in the late Fourth Century and the refounding of Chester as an Anglo-Saxon burgh in 907
- The walls were extended when a castle was built following the Norman Conquest in the 11th Century
- Their last military use was during the English Civil war when the city was under siege by Oliver Cromwell's forces
Source: Chester: A History - Simon Ward