A city council has said it would be "seeking answers" after vehicles were left dangling from the edge of a partially collapsed car park.
Part of a wall came away at the NCP Nottingham City Car Park in Cumberland Place in the early hours of Saturday.
Nottingham City Council said it wanted "assurances about the safety of NCP's other car parks" in the city.
NCP said how it happened was yet to be established and it was "undertaking a thorough internal investigation".
No-one was injured and no cars were damaged in the collapse.
The front fascia had "fallen" off the privately-owned car park, which has 500 spaces, blocking the entrance and exit.
It left three vehicles hanging over the edge of the car park from a floor roughly 50ft (15m) above the ground.
They have since been removed but there are still cars inside on some of the lower floors.
Leader of Nottingham City Council, Councillor Jon Collins, said: "It's shocking that such a major structural failure can have occurred in this way.
"The car park is run by NCP but clearly the council... will be seeking answers about what happened as quickly as possible and assurances about the safety of NCP's other car parks in the city."
In a statement it said: "NCP is undertaking a thorough internal investigation, have informed the landlord, and will co-operate with any investigation conducted by the regulatory authorities.
"At this early stage it is inappropriate to comment any further."
The operator said the car park would "remain closed until further notice" and has advised customers to use the nearby St James's Street Car Park.
A spokesperson for the Health and Safety Executive said: "HSE has been made aware of the incident and is making initial enquires."