One person has been killed and seven others injured in a series of stabbings in the city of Birmingham early on Sunday.
"We can now confirm that we have launched a murder investigation following last night's events," West Midlands Police said.
"A man has died and another man and a woman have suffered serious injuries. Five others have also been injured."
Britain's Foreign Secretary Dominic Raab said he had no information to indicate the incidents were terrorism-related but the public should stay "very vigilant".
West Midlands Police were called to reports of a stabbing in Birmingham city centre at approximately 12:30 am (local time) on Sunday.
"A number of other stabbings were reported in the area shortly after," they said in a statement.
Police cordons were in place on Sunday morning in three separate locations in the city centre: Hurst Street, Irving Street and Edmund Street.
West Midlands Mayor Andy Street said the series of incidents in the Hurst Street area of the city centre appeared to be related but the motivation for them was not yet understood.
"At this early stage it would not be appropriate to speculate on the causes of the incident," the police said.