A man has died after police used CS spray during a violent incident in Belfast city centre.
The man had been in a critical condition in hospital.
The trouble happened near the Grand Opera House at about 5am on Thursday and a defibrillator was left at the scene.
The Police Ombudsman is investigating and said police were called after a man was suspected of involvement in an altercation with taxi drivers.
In a statement on Thursday evening, they said: "The man who became unwell during an incident involving police officers in Belfast City Centre this morning has died.
"The incident, during which police officers used CS Spray against the man, is currently being investigated by the Police Ombudsman’s Office.
"The PSNI were called to Great Victoria Street at around 5am following an alleged clash between the man and taxi drivers.
The area was cordoned off and a section of Great Victoria Street was closed for a time but has been reopened.
Investigators have mapped and photographed the scene, security camera footage has been recovered and enquiries are ongoing to acquire further footage.
A number of witnesses have been spoken to but the office has issued an appeal for anyone else who was in the area at the time and may have seen what happened to contact them.
Speaking from the scene, senior Police Ombudsman investigator Paul Murphy said: "It is believed CS spray was used during the arrest of the man and at some point during that arrest that man's condition deteriorated.
"Because somebody has been arrested - and is in effect in police custody - and has suffered a potential injury and is critical in hospital it is a matter for the ombudsman to carry out an investigation and to establish the facts of the arrest and if CS Spray has been used and the potential use of force."
The investigator said evidence was being collected and statements taken. He appealed for any witnesses to contact his office.
Police said they would not be commenting further and have referred the press to the ombudsman.