Eight men have been arrested on suspicion of murder after two teenage boys died.
Essex Police said officers found three people injured after receiving a number of calls to Regency Court, Brentwood, at about 01:30 BST.
Two of those had since died, the force said, while the third was treated for non-life threatening injuries.
Brentwood and Ongar’s Conservative MP, Alex Burghart, called it a “very dark day for our town”.
Police said they were “working to establish how the boys died” and post-mortem examinations would take place.
The BBC understands the boys are suspected to have suffered stab wounds.
Det Ch Insp Andy Clarkson, of the Kent and Essex Serious Crime Directorate, said: “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.”
The detective said the incident “required an immediate and a large-scale response” and that investigations would continue throughout Sunday.
He added: “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 01:00 and 02:00 to come forward and speak to us if you have not already done so.”
Mr Burghart said: “This a very dark day for our town. My deepest condolences to the families of the boys who have so dreadfully lost their lives.
“I must urge anyone with any information to immediately share it with the police so that justice can be done as swiftly as possible.”
Ch Insp Mark Barber added there would be a “highly-visible police presence” in Brentwood on Sunday.
“I am acutely aware that this incident will shock many within the community,” he said. “My officers will be there throughout the day – they will be there to reassure you and keep you safe.
“If you have any concerns or information on the incident then, please, do not hesitate to come forward and speak to them.”