The Police Ombudsman for Northern Ireland is investigating an incident during which a man was shot in the chest by police.
The incident happened at around 10.45pm last night in the Waterside area of Derry.
Police responded to a report of concern for the safety of a man at an address at Celandine Court at Gobnascale.
The PSNI said that as officers were dealing with the incident, a police firearm was discharged and a man "sustained a chest injury".
The man was taken to hospital where he is understood to be in a critical condition.
A police officer also sustained stab wounds to his arm and head during the incident and he was taken to hospital to be treated for his injuries.
A spokesman for the Police Ombudsman's Office said that investigators are at the scene and are making inquiries to establish what happened.
The spokesman said that police went to a flat after receiving a call for assistance.
"There was then a confrontation during which one police officer sustained stab wounds and police discharged CS spray and a single gunshot".
"Police notified the Police Ombudsman's on-call team about the incident, and our investigators have been making inquiries at the scene throughout the night.
The Police Ombudsman has appealed for anyone who knows anything about what happened or who can assist in their inquiries to contact them.
The witness appeal line is 0800 032 7880.
The Chair of the Police Federation for Northern Ireland has described the events as a "horrific incident for all concerned".
Mark Lindsay has also called for a more widespread roll out of tasers to deal with potentially life-threatening incidents.
Mr Lindsay said that tasers "protect lives and prevents injuries" and said they should be seen as a "preferable option" to a firearm.
Sinn Féin MLA Martina Anderson said she is "deeply concerned" about the shooting.
She said she hopes the man involved will survive his injuries and that the police officer who was injured makes a full recovery.
Ms Anderson said the PSNI needs to provide a full explanation about this shooting and that she has contacted the Police Ombudsman to convey her "grave concerns".
SDLP leader Colum Eastwood tweeted "Worrying news that a man was shot and a police officer injured in Gobnascale last night. The Police Ombudsman needs to carry out a thorough investigation into this incident."