A man shot and killed a woman then returned to the same neighbourhood hours later and shot four more people, killing a journalist covering the original shooting and a nine-year-old girl, police in Florida have said.

Orange County Sheriff John Mina characterised the shootings in Orlando on Wednesday as random acts of violence. Mr Mina said during a news conference that 19-year-old Keith Melvin Moses has been arrested and charged with first-degree murder in the initial shooting that killed Nathacha Augustin, 38, and that “numerous more charges” would follow.

Spectrum News 13 identified the dead reporter as Dylan Lyons. Photographer Jesse Walden was also wounded. Mr Mina said Walden has been talking to investigators while being treated at a hospital.

The two were in an unmarked news vehicle on Wednesday afternoon covering the first homicide when a man approached and shot them, Mr Mina said.

The man then went to a nearby home where he fatally shot T’yonna Major and critically wounded the girl’s mother. Officials have not released the mother’s name.

Mr Mina said on Thursday that investigators do not know the motive for any of the shootings.

He said Moses is a known gang member but that the shootings did not appear to be gang-related.

It was not clear if Moses knew that two of the victims were journalists and noted that their vehicle did not look like a typical news van or have the station’s logo on it.

The sheriff said when deputies arrested Moses, they seized a Glock semi-automatic weapon that “was still hot to the touch, meaning it had just been fired, and there were no more rounds”.

Moses complained he was hurt and was taken to a hospital where he attacked medical staff, Mr Mina said. He has since refused to speak with detectives.

It was not immediately known whether Moses has a lawyer who can speak on his behalf.

A man who called 911 after Ms Augustin was shot told investigators that he was driving around smoking cannabis with her when he spotted Moses walking along a road.

He said Moses “seemed down” so he offered him a ride, according to an arrest affidavit.

Moses climbed into the backseat, behind Ms Augustin, and about 30 seconds later the driver said he “heard a loud bang” and saw blood on Ms Augustin’s face.

He said he stopped and Moses fled. The driver called 911.

He told investigators that Moses and Ms Augustin did not know each other and that he did not hear the two exchange any words before the shot was fired.

Mr Mina said on Thursday that the driver and Moses are cousins.

Deputies went to the Pine Hills area, just north west of Orlando, at about 11am on Wednesday after reports that a woman in her 20s had been shot.

About five hours later, 911 calls began coming in from the same scene, the sheriff said. Police found the journalists who had been shot being helped by a news crew from another station, WFTV.

“I want to acknowledge the brave WFTV news crew who was there and witnessed the shooting and rendered aid to the victims until our deputies arrived,” Mr Mina said.

Lyons was born and raised in Philadelphia, and graduated from the University of Central Florida, the station said. Before joining Spectrum News, he worked for a station in Gainesville.

“(Lyons) took his job very seriously. He loved his career. He loved what he did,” said Spectrum Sports 360 reporter and friend, Josh Miller.

“He loved the community, telling the stories of people, reporting on the news, and he was just passionate about what he did.”

Rachel Lyons, the reporter’s older sister, is raising money for his funeral via GoFundMe. She wrote that Lyons would have turned 25 in March. He is also survived by his parents and fiancee.

State Attorney Monique H Worrell said at a news conference on Thursday that her office had received multiple calls asking why Moses was not in custody from previous offences.

“This individual’s only adult offence was a possession of marijuana, 4.6 grams of marijuana, that my office did not charge because when you have a quantity that low, the Florida Department of Law Enforcement does not test the substance, and that means the state’s attorneys office cannot prove the case,” she said.

Ms Worrell said she was prohibited by Florida law from discussing any juvenile charges the man might have faced.

Earlier in the news conference, Mr Mina said that Moses had faced at least two gun-related charges as a juvenile including possession of a firearm by a minor and robbery with a deadly weapon.

Karine Jean-Pierre, the White House press secretary, said “our hearts go out” to the families of those killed in yesterday’s shooting.

“Too many lives are being ripped apart by gun violence,” she said. “The president continues to call on Congress to act on gun safety, and for state officials to take action at the state level.”