There are conflicting reports about the shooting, which happened during a second night of unrest in Charlotte, North Carolina. Police used tear gas and rubber bullets to disperse angry demonstrators.
Charlotte city officials confirmed that a man suffered gunshot wounds during Wednesday evening's protests, and was on life support and in a critical condition.
They contradicted an earlier report that the man had died from the shooting incident, which happened when a peaceful rally against the fatal police shooting of a black man on Tuesday turned violent.
Police officials said the latest shooting victim had not been wounded by a police officer.
North Carolina governor Pat McCrory later declared a state of emergency in Charlotte due to the unrest, a statement from his office said.
Wednesday's protest got out of control after several hundred demonstrators approached a downtown intersection and began to surround and taunt groups of police and their patrol cars.
Some protesters banged on glass windows, others threw objects at police and stood on cars as police fired tear gas and rubber bullets, prompting demonstrators to run. Protesters were also seen looting a convenience store after smashing its windows.
Seven law-enforcement officers and one civilian were also taken to hospital for injuries sustained during the protests, city council official Kenny Smith said.
Outrage in black community
The trigger for the violence was the killing of Keith Lamont Scott on Tuesday, who was shot dead in an apartment complex car park. The 43-year-old had been stopped by officers searching for a suspect.
Police said Scott was armed and ignoring officers' orders when he was gunned down, while the victim's family and a witness said he was holding a book, not a weapon.
Within hours of his killing, protesters had taken to the streets, clashing with police in riot gear. Sixteen officers were injured late on Tuesday and early Wednesday.
Authorities have not released any video of the incident, but the city's mayor said they plan to do so.
A string of fatal police shootings in recent months - from Baton Rouge, Louisiana to St. Paul, Minnesota - has left many Americans demanding law enforcement reforms and greater police accountability.
mm/kl (AP, AFP, dpa, Reuters)