A man has died and two men have been taken to hospital with life-threatening injuries following reports of an aggravated burglary, police said.
Avon and Somerset Police were called to a property on Prewett Street in Bristol at 1.06am on Monday and are now conducting a murder inquiry.
The force said officers, responding to reporting of an aggravated burglary in process, found several people had been assaulted.
One man died at the scene as a result of injuries sustained in the incident, it said.
Two other men have been taken to hospital with life-threatening injuries.
Two men from London, aged 25 and 37, have been arrested on suspicion of murder and are in police custody.
A cordon is in place and is likely to remain “for some time” to allow specialist crime scene investigators to examine the area, police said.
Police have closed one side of the A38 Redcliffe Hill – a main arterial route around Bristol city centre – causing significant traffic disruption.
A tent had been erected outside Canynge House on Prewett Street – a block of flats adjacent to Redcliff Hill.
Scenes of crime officers were seen taking photographs and loading evidence bags into their vehicles.
Senior investigating officer Andrew Mott said: “We deployed a significant number of resources to this incident and, as a result, we’ve apprehended two men who ran away from the scene when we arrived.
“This is now a murder inquiry and the public will see a significantly increased police presence in the area with detectives and staff examining the scene and neighbourhood officers conducting extra reassurance patrols.
“Early indications are that this appears to be an isolated incident but I’d urge anyone with concerns to speak to one of the neighbourhood officers.
“Although we’ve made two arrests, we’d still like to speak to anyone who had information about this incident.
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“Did you see or hear anything suspicious in the Prewett Street last night or in the early hours of this morning?
“Do you know anything about the events which led to this incident?”
Anyone with information is asked to contact the force on 101 giving the reference 5218139404.