Five people have been injured in two linked stabbing incidents in a city centre.
Four people have been arrested - two in connection with attempted murder - after the fights, which took place in Sheffield early on Saturday morning, South Yorkshire Police said.
The force said the incidents were not terrorism-related, adding that officers believe they are linked and possibly involve the same local individuals.
The first fight was reported to police at about 4am, and one person was arrested, and then a t 5.53am officers received reports of another brawl in Cambridge Street, in which three people were stabbed and a man was hit over the head with a bottle.
A police statement said: "Five people are confirmed as injured, with one person in a serious but stable condition in hospital.
"Four people have been arrested and are now in police custody. Of these four, two have been arrested in connection with attempted murder, and two in connection with public order offences."
The force said a number of streets remain closed off until further notice, including Cambridge Street, Carver Street/Division Street, and Barker's Pool, and there is no access to Bethell Walk.
Beer barrels inside the cordon had what appeared to be police riot shields placed on top, with blood on the surrounding pavement.
Forensics officers could be seen closely examining the shields and items within the cordon.
The scene is at the heart of Sheffield's night life, and is close to the city's main war memorial and John Lewis store.
Police are appealing for anyone who may have witnessed the incidents, or who has any information, to call them as soon as possible on 101 or contact Crimestoppers anonymously on 0800 555111.
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