A police officer has been left with a potentially life-changing injury in a central London attack that also saw her colleague stabbed in the neck.
The stabbing near Leicester Square at 06:00 BST is not related to the Queen's death or terror-related, police say.
Mayor of London Sadiq Khan branded the incident "utterly appalling" at a "momentous time for our country".
A man in his 20s has been arrested on suspicion of grievous bodily harm and assaulting an emergency worker.
The female officer was stabbed in the arm before her male colleague ran after the "frenzied" suspect and a tussle ensued, Met Police Commissioner Sir Mark Rowley said.
The male officer was "very seriously injured" after being stabbed three times in the neck and once in the chest but should make a full recovery, he added.
Other colleagues joined and fired a Taser at the suspect during the "violent struggle" on Great Windmill Street, near Shaftesbury Avenue. He was subdued then arrested, Sir Mark said.
He has since been discharged from hospital into police custody.
The officers' families have been told about the "very concerning" attack, Scotland Yard said.
Praising the officers' bravery, Sir Mark said: "It's a reminder to me that with all the calls for reforming the Metropolitan Police, which are absolutely necessary, we should never forget that we've got thousands of dedicated men and women going out every day who are prepared to be brave for Londoners."
The stabbing took place close to Haymarket, between Leicester Square and Piccadilly Circus, which is home to many of London's theatres and Chinatown.
By Jay Gardner, BBC London
Leicester Square, an area usually bustling with commuters and tourists, is almost completely inaccessible to the public.
Police lines stretch from Haymarket south to Leicester Place, with the northern half of the square completely shut off.
Several police officers are patrolling the cordon, with the strongest presence on Coventry Street, near the junction with Haymarket.
In the no man's land between the police tape, there are a few police cars and vans. I also spotted an incident response vehicle left nearby.
There is a sense of confusion among those in area.
Shop owners tell me they came to work and saw the police setting up the cordon, but eyewitnesses are hard to come by as it seems the attacks happened too early for anyone to see in an area famed for its nightlife.
Overnight, two other officers were injured, including one who was driven into by a car in south London, according to London's mayor.
Mr Khan said: "These brave officers were doing their duty and assisting the public at this momentous time for our country.
"My thoughts and prayers are with them, their loved ones and police colleagues following this disgraceful attack."
Home Secretary Suella Braverman said she was "concerned" about the attack and praised the bravery of police officers.
Martin Hewitt, the chair of police chiefs, described the attack as "terrible news".
According to Home Office data, 11,730 constables were assaulted with injury across England and Wales during the year ending March 2022, a rise of 3% from the 12 months before, although this does not include the most serious cases.
Some 2,800 Metropolitan PCs were assaulted with injury during the year ending March 2022 – almost a quarter of the total.
Follow BBC London on Facebook, Twitter and Instagram. Send your story ideas to [email protected]
Nation pays final farewell to Queen Elizabeth II
How the world watched the Queen's funeral
'I lost my home to floods – my baby could be next'
Far-right leader scents power in divided Italy
'I lost my home to floods – my baby could be next'
What did China say about Russia? Take our timed quiz…
The village where a Christmas tree can be treacherous
Off-gridders take energy needs into their own hands
Daughter rises in India tycoon’s succession plan
France's field of 3,000 standing stones
The personal touches in Her Majesty's colourful wreath
Watch moments from the funeral of Queen Elizabeth II. Video
Four cities saying no to cars
The biggest myths of the teenage brain
The jobs employers can't fill
© 2022 BBC. The BBC is not responsible for the content of external sites. Read about our approach to external linking.
