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A party in Camden was reported to the council by worried residents hours before a weapon was fired into a crowd injuring four people.
The party began Saturday lunchtime with a barbeque at Clarence Gardens on the Regents Park Estate.
Speaking anonymously, one resident told ITV News London neighbours called to complain about loud music, drinking and apparent drug use.
"The party started around 1pm, seemed like a handful of maybe 20 people. Loads of different vehicles coming in. It wasn't just a small barbeque. Speakers were playing really loud music," the resident said.
"Around 4 or 5 o'clock lots of neighbours started to phone Camden Council and they said they would send a patrol. I saw the patrol come into the estate and drive straight out," she added.
A 19-year-old woman; a 17-year-old woman; a 28-year-old man and a 73-year-old woman were injured, none of their injuries are thought to be life threatening.
"Residents are the eyes and ears of our estate, we know what looks like a genuine, innocent event and what looks like something that will end in a really bad way," the woman said.
"This wasn't a good party. The music they were playing, what they were doing. Smoking, loads of alcohol, littering - it was far more than just a noise nuisance call.
"Tensions were high. It was a big group of people, getting bigger and bigger and bigger as the day went on," she added.
Police said up to five men arrived at the party and "indiscriminately discharged a firearm".
Detective Superintendent Caroline Haines, acting BCU Commander for Camden and Islington said: "Like many members of the community I am shocked by this incident and my thoughts are with the friends and family of those injured.
"I know that the local community have understandably been deeply unsettled by this and I want to reassure residents that our investigation is continuing at pace.
"We are progressing various lines of enquiry and we are working around the clock to bring those responsible to justice.
"Local residents should expect to see a heightened police presence in the area as we continue our work."
Camden Council said it was "incredibly distressed" that a shocking act of violence happened in the community.
Councillor Georgia Gould, Leader of Camden Council added: "My thoughts are with them, their family and friends. Cllr Shah, the Community Safety Cabinet Member, and I visited Clarence Gardens on Sunday to hear from residents and the community.
"Clarence Gardens and the wider Regents Park Estate are at the heart of our Borough – a diverse and tightknit community of families and young people, people who have made their home there for decades, community leaders and civic activists.
"I know many residents may have concerns about their safety after the events of Saturday night and I, Cllr Shah and the Council will do all we can, working with the Police, to provide comfort and assurance in the days and weeks ahead."