Three people, including a police officer, have been stabbed in London's Hyde Park after a water fight got out of control.
A second police officer was wounded by a bottle.
The officers are in hospital and their injuries are not life-threatening.
The other two people were both taken to hospital. One has injuries that are not life-threatening but the condition of the second is unclear.
Police were at the park's Serpentine from 3pm after a large number of people gathered for the water fight.
A Met Police spokesman said that at about 8.40pm parts of the crowd became "hostile" and began to throw things - including bottles - at officers.
Officers stayed at the park until the crowds had left by around 2.20am the following morning.
It is not yet clear what sparked the trouble but some people who said they were at the gathering blamed police.
Disorder in #HydePark one officer injured @MPSWestminster on scene and dealing https://t.co/cj7lAFt3DC pic.twitter.com/9cCibav4pU
— Metropolitan Police (@metpoliceuk) July 19, 2016
Eyewitnesses
One Twitter user, @imanilindsay, said she thought there had been no problem before the police arrived.
She wrote: "I do not in any way condone the throwing of bottles. I cried when it happened.
"I have an issue with how the teens were lured into a trap.
"It was like watching an animal being back up against a wall and playing on the fact that it reacted."
She added: "They got what they wanted ... to get the Black people out of the park."
But a video posted on an account called @YT_Bricks showed parts of the incident and someone can be heard saying:
"They are throwing bottles at Fed cars...they are mashing up the Fed cars".
Police say they have not yet made any arrests but asked anyone with information to contact them.
