The shooting occurred in the early hours of Monday when officers confronted two men sitting in a Honda that had been reported stolen.
"I ask everyone to not rush to judgment and allow the investigation to be completed," Sheriff Jerry Demings, himself black, said flanked by black religious and community leaders.
The victim was last night in a critical condition in hospital.
There were fresh protests in several US cities, most notably Berkeley, California, where crowds briefly blocked a major road and forced the closing of an underground train station. Police arrested nine people.
The protests started when, last month, a grand jury in St Louis declined to indict the police officer who killed Michael Brown in Ferguson, Missouri, last August.
They were rekindled last week when a New York grand jury similarly absolved the officer involved in the stranglehold death of Eric Garner.
Obama's response under scrutiny
There is frustration that US President Barack Obama has not seemed able or willing to respond with more passion to the events.
Mr Obama attempted to repel that perception in an interview with the BET television network.
"I'm going to stay on this," he said. "Not only am I going to stay on it ... but hopefully the entire society says, 'Let's finally try to make some real progress on this'."
Witnesses to the Orlando shooting said the victim, identified by police as 28-year-old Cedric Bartee, had his hands in the air when the officer who had approached the car opened fire.
"His hands went down after the first shot," Natasha Hall, a resident in a nearby apartment complex told the Orlando Sentinel newspaper.
While promising a swift investigation, Mr Demings said Mr Bartee had failed to comply with police commands.
He said the officer, Sergeant Robert McCarthy, had become fearful for his life after Mr Bartee appeared to engage in "extensive furtive movements" inside the car.
Mr Demings said he was striving to offer as much transparency as possible "because of the backdrop of everything happening in the country at this time".
Read next: Racial turmoil sweeps US
- Independent
