The governor of North Carolina has declared a state of emergency in the city of Charlotte, sending in the National Guard, as unrest over a police shooting continues.Violence erupted for a second night as protests over the killing of a black man spun out of control. One protester is in a critical condition after a ‘civilian on civilian’ incident, the city said.Riot police used tear gas as they faced hundreds of protesters, reports BBC. The demonstrators are angry that Keith Lamont Scott, 43, was killed by police on Tuesday.Police say Mr Scott was repeatedly told to drop his handgun before he was shot but his family say he was reading a book at the time.Sixteen police officers were injured in unrest on Tuesday night.Bottles and fireworksGovernor Pat McCrory declared the state of emergency as rioters attacked journalists and other people, breaking windows and setting small fires. The second night of protests had begun peacefully but the demonstration was interrupted by gunfire and a man in the crowd was injured. The city initially said he had been killed but then issued a clarification on Twitter.Protesters then threw bottles and fireworks at the officers, who were lined up in riot gear. Police fired flash grenades and tear gas to repel the crowds.The use of lethal police force against African Americans has been the subject of nationwide protests across the US for two years.