A disgruntled US employee walked back into the factory that fired him and fatally shot five ex-colleagues, before killing himself, police said.
John Robert Neumann, aged 45, was armed with a semi-automatic handgun and hunting knife when he entered the business near Orlando, Florida, on Monday morning. The US army veteran was sacked in April, police said.
There is no suggestion he was a member of a subversive or terrorist organisation, they add.
Orange County Sheriff Jerry Demings said the shooting had unfolded at the premises of Fiamma, which makes awnings for motor homes and camper vans. Most of the victims were shot in the head, some multiple times, he added.
"He was certainly singling out the individuals that he shot," said Sheriff Demings.
The victims included Robert Snyder, aged 69, Brenda Montanez-Crespo, aged 44, Kevin Clark, aged 53, Jeffrey Roberts, aged 57, and another unidentified man.
Neumann reloaded his handgun at least once during the rampage, the sheriff said.
The gunman had told an employee whom he did not know to leave the premises, and left about seven other staff members uninjured.
Neumann - who lived alone in the area - killed himself as deputies were about to enter the warehouse, the sheriff said.
Authorities said that he did not have a permit for the weapon.
He was honourably discharged from the army in 1999. He had a history of misdemeanour criminal offences, such as possession of marijuana and driving under the influence.
Neumann attacked a member of staff in 2014, though no charges were filed, police said.
In a statement, Florida Governor Rick Scott condemned a "senseless act of violence".
"Over the past year, the Orlando community has been challenged like never before," he said.
The shooting came a week before the first anniversary of the Pulse nightclub shooting that left 49 people dead in Orlando.
In last June's attack, the deadliest mass shooting in modern US history, gunman Omar Mateen killed 49 people and injured dozens more at a gay nightclub before being shot dead by police.