Matt Ratana. Photo / Facebook
The police officer shot dead while on duty in south London also served in New Zealand.
Sergeant Matiu Ratana, known as Matt, died at Croydon Custody Centre at 2.13am local time after he was shot by a person being detained.
New Zealand Police Commissioner Andrew Coster said he joined the NZ police in 2003 as part of the British High Commission Wing, Wing 212.
Father-of-one Ratana was two-months away from retirement, UK media reported.
"He served in Auckland City and Counties Manukau until 2008, before returning to the UK," he said.
"As my counterpart, Commissioner Cressida Dick of the Metropolitan Police, has expressed this morning, policing is a family.
"While Sergeant Ratana spent most of his career in the UK, anyone who serves here will always be a part of our New Zealand Police whānau.
"We send our condolences to his friends and family here and abroad, and his colleagues in the Metropolitan Police and across the UK who will be deeply feeling this loss today."
Ratana was already an experienced police officer when he joined the New Zealand force, joining the Metropolitan Police (Met) in 1991.
Dick confirmed the tragedy earlier this morning (NZ time).
"It is now my sad duty to confirm that our colleague who was killed was 54-year-old Matt Ratana, a custody sergeant," she said.
"As a colleague, he was big in stature and big-hearted, a friendly, capable police officer.
"A lovely man, highly respected by officers and staff, and by the public, including suspects he arrested or dealt with in custody."
He is survived by a partner and an adult son from a previous relationship.
Friends, family, workmates, and members of the public are all paying tribute to the expat Kiwi.
East Grinstead RFC, where Ratana was their head coach, said they were "utterly devastated" to hear he had died.
"Matt was an inspiring and much-loved figure at the club and there are truly no words to describe how we are feeling," club chairman Bob Marsh and president Andy Poole said on the club's Facebook page.
"We would like to take some time as a club and community to begin to comprehend what has happened.
"Our deepest and sincerest condolences go to Matt's loved ones, family, friends, colleagues and to our community rugby family at this most terrible time."
Ratana went to school at Palmerston North Boys' High School before attending the University of Otago where he played for Ravensbourne RFC.
Palmerston North Boys' High School said Ratana was at the school from 1980 to 1985.
"Matt was a school prefect, an outstanding tennis player, the school tennis champion in1985, and a Manawatū tennis representative," the school said.
"Matt also played in the school 1st XI football team in 1985.
"Our thoughts and condolences go out to Matt's family and friends at this terribly sad time."
New Zealand Prime Minister Jacinda Ardern has also paid tribute to Ratana, taking to Facebook to pass on her sympathies to his family.
"Incredibly sad to hear [the] news this morning that a Metropolitan Police officer killed in the UK was Matiu Ratana, a former New Zealand Police officer," she said.
"Sergeant Ratana worked in Auckland City and Counties Manukau until 2008, before returning to the UK.
"To all Matiu's whanau across the world, we share your sorrow and have all our condolences."
Ratana was well known in the local rugby community, Park House Football Club said on Facebook, and their thoughts were with his family and friends.
Sadiq Khan tweeted, on the Mayor of London's official Twitter account, Ratana's bravery and sacrifice would never be forgotten.
"I want to extend my heartfelt condolences to the family and friends of Sergeant Matt Ratana who tragically lost his life while on duty," the tweet said.
Earlier, Khan said he was devastated by the news an officer had been killed.
"Tragic incidents like this are terrible reminders of the dangers our police officers face every single day they go to work to keep Londoners safe," he said.
Prominent UK broadcaster Piers Morgan also paid tribute to Ratana on Twitter, thanking him for his nearly 30 years of service as a police officer.
"An absolute tragedy. Thank you for your service Matt."
Tributes are being posted to his personal social media accounts, too.
"RIP Matt - will miss our chats. Wonderful mate and colleague, a true gentleman. Sympathy and love to all your family and friends. God Bless Top Man,' a Facebook user said.
"R.I.P Matt. Your spirit will live on. Thoughts with all your family, friends and colleagues," another said.
Elsewhere, on his Instagram account, users are commenting with love heart emojis on his latest post.
New Zealand Police Minister Stuart Nash thanked Ratana for his decades of service in both Aotearoa New Zealand and in the UK.
"A sad day for the @nzpolice too, & former colleagues still serving. Condolences to whanau," Nash tweeted.
Former National party leader and current MP for Tauranga Simon Bridges has also paid tribute to Ratana on Twitter.
"Awful news. So many Kiwis travel the world and devote their lives to the communities they make their home," he said.
"My thoughts are with Matt's family over there and here in New Zealand."
Recently, Ratana had been a coach at East Grinstead Rugby Club where friends have described him as "inspirational" and "larger than life".
"He helped out at the club a lot. We lost funding and he came in and helped us," Ratana's friend, Paul, told Sky News.
"He was inspirational - so vibrant, so bubbly, larger than life. He will be a huge loss to the club.
"The man was a machine. He was at training last night from 7 to 9pm. That's the last time I saw him. He was due to retire soon and was looking forward to it."
Police stations across the UK are flying their flags at half-mast and officers also held a minute silence to honour Ratana.
'Police cannot rule out the possibility of further arrests and charges.'