Eight people have been arrested on suspicion of murder after the deaths of two teenage boys.
Despite attempts to save them, two died. The third victim was treated for injuries which police said are not life-threatening.
No cause of death has been given and post-mortem examinations will be carried out.
The families of the victims have been told.
Detective Chief Inspector Andy Clarkson, of the Kent and Essex Serious Crime Directorate, said: “This incident has required an immediate and a large-scale response and officers and investigators have worked through the night to piece together what happened in the lead-up to this tragic incident.
“Our investigations will continue throughout today.
“We understand there will naturally be shock and concern within the community after such a tragic loss of life, but at this stage we do not believe there is any wider threat to the public.
“We know there were a number of witnesses to this incident and I would urge anyone who saw anything in Regency Court and the roads around it in central Brentwood between 1am and 2am to come forward and speak to us if you have not already done so.”