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Three people were hurt by an unknown liquid and two others trampled as panicked crowds fled after fears of an “acid attack” at Notting Hill Carnival.

Police said three people were treated for skin irritation after being targeted with the unknown liquid at just before 8pm on Sunday – the first day of the west London festival.

Two others were injured as crowds quickly sprinted away from St Charles Square where the alleged acid attack happened. Nobody has yet been arrested but Scotland Yard said an investigation is ongoing.

Crowds at this weekend’s carnival have been on high alert after fears acid attackers could target festival-goers. It follows a rise in the number of acid attacks, mainly across east London, in recent months.

On Monday, footage emerged of terrified crowds fleeing through a street near Ladbroke Grove in a panic.

The video clip, recorded from the event on Monday evening, shows screaming revellers sprinting away as whistles can be heard blowing in the background.

Notting Hill Carnival 2017 - day two 21 show all Notting Hill Carnival 2017 - day two 1/21 Two women wave for the cameras at the start of day two of Notting Hill Carnival REUTERS 2/21 Carnival performers parade in the sunshine on the main Parade day of the Notting Hill Carnival AFP/Getty Images 3/21 Hot stuff: Carnival-goers bask in what was predicted to be record levels of heat PA 4/21 A woman dances in the sunshine at Carnival Rex Features 5/21 A carnival performer poses for photos AFP/Getty Images 6/21 A woman blows kisses to the camera as parades get underway on the second day of carnival AFP/Getty Images 7/21 Carnival performers parade in the sunshine AFP/Getty Images 8/21 A woman dances in the parade on day two of the 2017 Carnival REUTERS 9/21 A woman gives a cheeky wiggle for photographers REUTERS 10/21 Performers make their way to the start of the parade on the second and final day of the Notting Hill Carnival PA 11/21 Dancers head to Carnival on the Tube Rex Features 12/21 A dancer bares (almost) all ahead of the second day of Carnival PA 13/21 There will be further commemorations for the Grenfell Tower victims later today PA 14/21 Police officers pass performers ahead of the second day of Carnival PA 15/21 Dancers from the Paraiso School of Samba observe their own minute's silence in memory of the victims of the Grenfell Tower fire PA 16/21 Performers prepare to take part in the parade PA 17/21 Two women make their way to the start of the parade PA 18/21 Juliana Campos and her nine-year-old daughter practice their moves before the start of the celebrations PA 19/21 Four women in burlesque outfits get ready to wow the crowds at carnival PA 20/21 Samba dancers prepare for their big day in the sun Rex Features 21/21 Four dancers get ready to take part in the Carnival parade Rex Features 1/21 Two women wave for the cameras at the start of day two of Notting Hill Carnival REUTERS 2/21 Carnival performers parade in the sunshine on the main Parade day of the Notting Hill Carnival AFP/Getty Images 3/21 Hot stuff: Carnival-goers bask in what was predicted to be record levels of heat PA 4/21 A woman dances in the sunshine at Carnival Rex Features 5/21 A carnival performer poses for photos AFP/Getty Images 6/21 A woman blows kisses to the camera as parades get underway on the second day of carnival AFP/Getty Images 7/21 Carnival performers parade in the sunshine AFP/Getty Images 8/21 A woman dances in the parade on day two of the 2017 Carnival REUTERS 9/21 A woman gives a cheeky wiggle for photographers REUTERS 10/21 Performers make their way to the start of the parade on the second and final day of the Notting Hill Carnival PA 11/21 Dancers head to Carnival on the Tube Rex Features 12/21 A dancer bares (almost) all ahead of the second day of Carnival PA 13/21 There will be further commemorations for the Grenfell Tower victims later today PA 14/21 Police officers pass performers ahead of the second day of Carnival PA 15/21 Dancers from the Paraiso School of Samba observe their own minute's silence in memory of the victims of the Grenfell Tower fire PA 16/21 Performers prepare to take part in the parade PA 17/21 Two women make their way to the start of the parade PA 18/21 Juliana Campos and her nine-year-old daughter practice their moves before the start of the celebrations PA 19/21 Four women in burlesque outfits get ready to wow the crowds at carnival PA 20/21 Samba dancers prepare for their big day in the sun Rex Features 21/21 Four dancers get ready to take part in the Carnival parade Rex Features

One witness told the Standard she was on Portobello Road when the police started telling people to run.

Another festival-goer said: “I was on Ladbroke Grove and the floats were going past.

“A large amount of people started screaming and running towards where me and my friends were standing, and we ran in the same direction.

“We ran briefly and stopped. Then more people started running towards us and we kept running.

“We tried to ask the police we passed what was happening, immediately after, but they said they didn't know and were looking into it.”

A model who was at the carnival, and goes by the username Miss Fame on Twitter, said “everyone started to run”.

A spokesman for the Met Police said they are looking into what caused the panic but do not yet believe it was linked to any incident.

As of 3.30pm on Monday, some 149 arrests had been made - over a third of which, 61, were for drug offences, the Met said.

There were 17 public order arrests, and 15 arrests for possession of an offensive weapon, or knife/blade.