A police sergeant shot dead in Croydon was a New Zealander who had been working for London's Metropolitan Police for decades, Radio New Zealand is reporting.
The officer was shot at the Croydon Custody Centre, a police facility in the south of the British capital, in the early hours of Friday morning.
The Ministry of Foreign Affairs and Trade said it was aware of the incident, but at this stage could not confirm the victim was a New Zealander.
Tributes are appearing on the Facebook and Instagrams pages of the man believed to be the victim.
The sergeant was shot in the chest when a man, who was being detained, produced a gun during a search.
The police said the suspect, aged 23, then turned the gun on himself and was now in a critical condition after being treated for gunshot wounds.
He was also under arrest on suspicion of murder.
The policeman, understood to have been a few weeks away from retirement, was treated at the scene but later died in hospital.
The London Metropolitan Police commissioner Cressida Dick said: "We are all deeply shocked and very sad.
"I have visited and spoken to our officer's partner together with other colleagues, and we are of course giving her the best support we can. My heartfelt condolences go to her, to their family, to his colleagues and his close friends.
"A murder investigation is under way and officers are working at several crime scenes to secure evidence and to establish the facts of what happened."
The British Prime Minister Boris Johnson has paid tribute, saying: "We owe a huge debt to those who risk their own lives to keep us safe."
In a post on social media he added: "My deepest condolences go to the family, friends and colleagues of the police officer who was killed in Croydon."
The police said none of their weapons were fired during the incident.