Teenagers attacked police with bottles and knives in Hyde Park as the West End suffered the worst outbreak of youth violence since the 2011 riots.

Witnesses described how the Royal Park erupted into a “warzone” as hundreds of youths clashed with officers called after trouble flared at a water-fight and music party organised on social media.

Families and office workers enjoying the last of the evening sunshine scattered as more than a thousand teenagers fought running battles with riot police along the banks of the Serpentine, a few hundred yards from Kensington Palace.

The mob was driven back to Marble Arch where around 500 remained until midnight, hurling bottles at the ranks of police and chanting “Black Lives Matter”.

A breakaway group stormed a nearby branch of McDonald’s, causing terrified staff to flee downstairs as dozens of teenagers leapt over counters to clear the racks of food.

Buses were diverted from the streets around Park Lane, which was littered with shattered glass, as the last remaining youths were detained or dispersed.

Riot vans blocked off Oxford Street to prevent the crowd from spilling into the world-famous shopping district.

Two officers were rushed to hospital during the melee, one with stab wounds the other suffering head injuries after being struck by a bottle.

At least two other teenagers were taken to hospital with stab wounds.

There were unconfirmed reports of shots being fired.

Jon Paul Dorrian, 30, centre manager at Hyde Park tennis centre, said the crowds began arriving at around 4pm yesterday.

He said: “Later there were at least 1,000 young people down by the Serpentine playing music out of their speakers and the atmosphere seemed okay.

“There was a small police presence through the early evening but all of sudden, just before 9pm, there were officers everywhere. There were riot vans and police cars and bikes hurtling through the park.

“There were other people around them, tourists and people after work enjoying picnics with wine coolers. It was strange you turned from this picturesque scene and there were all these police driving back the group of young people.

“The group got angry. Some were shouting ‘black lives matter’. They were young and they were mostly intoxicated.”

Another witness said: “Two schools were supposed to have a water fight against each other but word got out and everyone just wanted to be involved

“When I arrived, there were just loads of people and police. Then a fight broke out. People were running towards us.

“My friend saw someone with a knife and said we need to leave because someone’s going to get shanked. Then all of a sudden people started running in waves.

“They were throwing bottles, two girls had a fight and it turned into madness.”

Another witness told the Standard: “I saw Hennessy bottles travelling at 100 mph at police vans. Random people who clearly wanted to cause trouble. I heard serious gunshots so I got out of there.”

Maisie May, who watched the scenes unfold, said: “It was a meet-up which happens there every year but it was definitely racially charged.

“It got out of control around 6pm when police began trying to disperse them. The crowd just got bigger and all moved towards the lake.

“They started throwing things at the police officers and cars, starting with plastic bottles but then glass bottles too. Police were chasing a man who apparently had a machete in and out of an area of trees.

“It was really intense and there were groups shouting ‘Black lives matter’ and things like that. It seemed like a rebound from what is happening in America. Police pushed them out of the park but they all gathered under Marble Arch.”

An eyewitness at Marble Arch said: “There was a huge crowd who were playing music and hanging around, they seemed like they were waiting for a confrontation.

“When the police began to move into the square to disperse them it kicked off, it was really scary, there were glass bottles smashing around the officers.

“A lot of people started shouting back at police, calling them ‘scum’ and hurling bottles. There were a lot of aggressive people storming around – the whole area just turned into a warzone.

“The police moved in on the crowd asking them to move on and that’s when it turned really nasty. People were throwing big bottles of whisky at police and you could hear girls screaming.

“People were getting arrested and everywhere you looked something was kicking off or a bottle was whizzing past.

“There were people revving quad bikes, a woman going crazy at police and throwing things in the street.

“The road was covered in glass. It just seemed to turn into a riot, it was chaos everywhere.”

Another witness said: “We came for the meet-up in the park but one guy stabbed another guy. Talking about that Black Lives Matter movement is rubbish when they go on this march and all this stuff and end up stabbing each other. It was drunkenness.”

A Met spokesman said: “Police in Westminster were in attendance at Hyde Park, by the Serpentine from 3pm after a large number of people gathered for a spontaneous water fight.

“At around 8.40pm, parts of the increasingly large crowd become hostile to police and items - including bottles - were thrown towards officers.

“Two police officers suffered injuries - one stabbed and one from a bottle. Both have been taken to hospital for treatment. Their injuries are described as not life threatening.

“Police are aware of two other people suffering stab wounds. Both have been taken to hospital and officers await an update on their condition.”

No arrests have been made and witnesses are asked to call police in Westminster via 101 or contact Crimestoppers on 0800 555 111 or at crimestoppers-uk.org