A gunman opened fire on two television journalists reporting on a murder near Orlando, Florida, on Wednesday, killing one and wounding the other before fatally shooting a 9-year-old girl and wounding her mother in a nearby home, authorities said.

A suspect identified as Keith Melvin Moses, 19, was arrested shortly after the assaults on the TV news team and the mother and daughter, about a block away from each other, in the Orlando suburb of Pine Hills, said Orange County Sheriff John Mina.

Moses was detained as a suspect in both those attacks and was formally charged in the killing hours earlier of a woman in her 20s, a shooting that the two journalists were covering when they came under fire, Mina said.

The sheriff described the two journalists as a reporter and a photographer for central Florida cable TV outlet Spectrum News 13, which is owned by Charter Communications.

None of victims was identified.

Mina said the suspect was armed with a pistol when taken into custody and has a lengthy criminal record that included arrests on charges of firearms offenses aggravated battery, assault with a deadly weapon, burglary and grand theft.

Mina said no motive had been determined for any of Wednesday's shootings, but he said Moses was believed to have been an acquaintance of the first victim, who was shot while sitting in a car with the suspected gunman and another person.

The sheriff said he did not know whether the two newsmen were targeted because they were journalists, adding that their automobile lacked the logos and markings typically seen on a news vehicle. They were in or near their vehicle when shot.

"As far as we know, he had no connection to the reporters and no connection to the mother or the 9-year old, and we don’t know why he entered their home," the sheriff said.

He said both the mother and the surviving journalist were in hospital in critical condition.

White House press secretary Karine Jean-Pierre posted a message of condolences on Twitter.

"Our hearts go out to the family of the journalist killed today and the crew member injured in Orange County, Florida, as well as the whole Spectrum News team," she said.