An estate agent and a customer had to be taken to hospital after they were plunged into the cellar of a property when the floor collapsed during a viewing.
The potential buyer was being shown around a derelict Grade-II listed property in Nottingham when the floor gave way.
The six-bedroom house, in Promenade, St Ann's, Sneinton, had been due to go up for auction on October 10 by estate agents Savills by order of Nottingham City Council.
The council has now launched an investigation into the incident.
Ambulance crews were called to the scene just before 5.30pm on Saturday to reports that two people had fallen through floor boards into the cellar of a property.
A spokeswoman for East Midlands Ambulance Service said: "Two patients were at the scene. A female reported to have head injuries and a male reported to have back pain."
Both were taken to the Queens Medical Centre for further assessment and treatment.
A Nottingham City Council spokesman said: "This appears to have been a terrible freak accident at a property we have been trying to sell which has been empty for a number of years.
"We're investigating how this happened and have secured the building until structural engineers have established what needs to be done to make sure the building is safe."
In a statement Savills, who are selling the property, said: "Two people were injured following an accident at a property located in St Ann's, Sneinton, Nottingham, over the weekend.
"Our first concerns are with the two people hurt, one of whom is a Savills employee. We wish them a full and speedy recovery.
"We are fully co-operating with the investigation into the cause of this accident and are working with Nottingham City Council, which owns the building, to understand the cause."