A man has died in hospital after being shot by police in the centre of Brighton.
Sussex Police said the shooting happened just after 1300 GMT in Rock Place.
The officers were on a pre-planned operation to find a man wanted in connection with a number of recent armed robberies, the force said.
The Independent Police Complaints Commission (IPCC) said what appeared to be a black handgun had been recovered.
An IPCC spokeswoman said: "This will now be examined to establish whether it is real or an imitation weapon and whether it had been fired."
One witness reported hearing two gunshots ring out before police tried to revive the dying man.
He was pronounced dead a short time later at the Royal Sussex County Hospital.
The man, believed to be in his 40s, has not been formally identified.
Frankie Sparrowhawk, 18, who walked past as it happened, said he heard two shots and saw a man on the floor.
He said: "There were five or six police officers there at that point.
"I was too far away to see if he was moving but it looked like one of them was trying to resuscitate him.
"An ambulance arrived within about two seconds."
Students at the Brighton Institute of Modern Music, which is just a few doors down from where the shooting happened, were ordered to stay inside by police.
After the shooting, police set up cordons and stood guard at each end of the narrow one-way street, which links the seafront with a busy shopping area. Traffic diversions were also put in place.
One resident, Janet Hood, 67, could not get back to her ground-floor flat in the street and said she was frightened and shaken up after the incident in what was "usually a very quiet street".
IPCC Commissioner Mike Franklin said investigators were at the scene.
He said: "This will involve taking initial accounts from those officers involved to establish which officer or officers fired and why, as well as identifying evidence on police systems such as incident logs and radio transmissions."
He also said the IPCC would speak to witnesses, examine CCTV footage and look at the pre-planning of the operation itself.
Supt Steve Whitton, of Sussex Police, said: "The armed officers were deployed on a pre-planned operation to locate a man wanted in connection with a number of armed robberies in Sussex over recent months."
He said the force "fully supported" the independent investigation.
A number of roads in the area have been closed, including a section of the A259 and diversions are likely to remain in place during the rush hour.
Motorists have been advised to avoid the area if possible.