Northern Ireland's police ombudsman is to investigate a video which appears to show two officers dragging an incapacitated woman from the middle of the road and leaving her in a bus lane.
The Police Service of Northern Ireland (PSNI) has said it will fully support the probe by ombudsman Dr Michael Maguire into the alleged incident in Londonderry.
The footage posted on the internet, said to have been taken in the city's John Street on St Patrick's Day on Monday, appears to capture two officers lifting a prone woman, who had been lying in the way of traffic, and placing her in a clearly marked area for buses to pull in.
The uniformed individuals then get into an unmarked car and drive off while the woman remained lying in the lay-by, only a few feet from the pavement.
The footage has provoked angry reaction from politicians in Derry, who claim police failed in their duty of care to take the woman out of harm's way.
A spokesman for Dr Maguire said: "The Police Ombudsman has this morning viewed video footage which appears to show what happens after two police officers discover a young woman lying on a road in Derry/Londonderry.
"Dr Maguire has now initiated an independent investigation into the police handling of the incident."
The ombudsman has asked for any witnesses to come forward.
PSNI assistant chief constable George Hamilton said the organisation expected its staff to behave " professionally, ethically and with the utmost integrity at all times".
"Any conduct, whether on or off duty, which brings discredit on the Police Service will be investigated," he added.
"This matter has been referred to the Police Ombudsman and we will fully support their investigation."
Stormont's Deputy First Minister Martin McGuinness, who lives in Derry, expressed his views on Twitter.
"Viewed video showing 2 police officers failing to ensure the safety of an incapacitated woman on a public roadway - totally unacceptable," he tweeted.
Foyle Assembly member Mark H Durkan said the footage will have shaken public confidence in the PSNI.
"Not only are these actions dangerous and irresponsible they are completely inhumane," the SDLP representative said of the alleged incident.
"I feel for the family of this girl. How can we believe that our young people are safe in our local community, when those who are charged with protecting them fall so far short of basic expectations?"
A spokeswoman for the PSNI's oversight body, the NI Policing Board, said:
"Whilst the circumstances surrounding this incident are not yet clear, video footage of the police response raises questions of the most serious nature.
"The Board and the public rightly expect the highest professional standards of all of our police officers and anything that falls short of that is simply unacceptable."