Four men are being hunted by police after a spate of stabbings and injuries during a night of violent clashes in London.
"Unacceptable" violence marred festivities as soaring temperatures gripped the capital on Tuesday, the hottest day of the year so far.
Police have released photographs of the suspects, three of whom are wanted in connection with violent disorder in Hyde Park and one over trouble in Marble Arch, and are also calling for anyone with footage of the incidents to come forward.
Three people, including a police officer, were stabbed at a water fight and unlicensed music event at Hyde Park. Four officers and a member of the public suffered other injuries.
In Burgess Park, south London, two 16-year-old boys were knifed and a nearby supermarket ransacked at an end-of-term water fight.
The disorder continued into the night when police were pelted with missiles at an illegal rave in north-east London.
Met Commander Nick Downing said police leave has been suspended to allow extra officers to patrol the streets until the weekend.
He added: "We are asking for the public's help to identify these four men, to give us any information they may have about anyone else who was involved in the disorder last night and, looking ahead, any information about future plans for such disorder.
"A lovely day in the capital turned violent in Hyde Park, Burgess Hill and Stamford Hill last night after spontaneous events turned nasty and people attacked each other and the police.
"Tonight, we've increased the number of police officers on duty, and cancelled any more leave so we keep extra officers out on our streets right through until the weekend."
London Mayor Sadiq Khan branded the violence "extremely disappointing" and said it was "probably fuelled by the hot weather".
The Hyde Park crowd, which police said peaked at around 4,000, gathered for a water fight by the Serpentine which turned hostile as the evening wore on.
The five officers were taken to hospital and have since been discharged, and the members of the public who were stabbed remain in hospital, where their conditions are not thought to be life-threatening.
Footage on social media showed people vaulting over the counter at McDonald's in Marble Arch, as crowds spilled out of the nearby park at around 9pm.
In Burgess Park, fights between small groups broke out just before 6pm which then escalated, and a crowd of between 1,000 and 1,500 people was dispersed by 11pm.
The two 16-year-olds who were stabbed suffered non life-threatening injuries. One remains in hospital.
At around 8pm police were called to a supermarket in Dunton Road, Southwark, to reports of up to 200 people causing damage inside the store and stealing, with two female customers suffering minor injuries.
Officers were pelted with bottles and other items as they interrupted a block party on the Stamford Hill Estate in Hackney. Some officers suffered minor injuries and three police vans were damaged.
On the previous evening, a 15-year-old girl was taken to hospital with suspected knife wounds to the head after hundreds gathered for a street party in St Mary's Road, Harlesden, north-west London.
Two women, aged 31 and 35, were arrested on suspicion of GBH at a nearby flat and taken to a north London police station.
Any witnesses are asked to contact the police on 020 8246 0076 or Crimestoppers anonymously on 0800 555111.