The mass shooting happened during the early hours at a billiards hall on a commercial estate near Miami Gardens, to the northwest of the coastal city's downtown.
CNN said about 20 to 25 of those injured were taken to a number of nearby hospitals.
A white SUV pulled up to the location and three people got out with assault weapons and handguns and started firing into the crowd that was gathered for a concert at the venue, USA news channel CNN reported.
The Miami Herald said 20 wounded victims were taken to local hospitals, and posted a photo of friends and relatives holding hands in prayer outside one trauma center.
"These are cold-blooded killers who fired indiscriminately into a crowd", he said, stressing, "We will do justice".More news: Horror: Remains of 215 children found at Canadian school site
"According to investigators, the establishment was hosting a scheduled event and several patrons were standing outside", Miami-Dade Police Department said in a statement.
One of those injured is in a critical condition, police say.
A search this week of the shooter's home - which was set ablaze shortly before the attack - turned up 12 guns, some 22,000 rounds of ammunition and suspected Molotov cocktails. "This is targeted. This is definitely not random", said Ramirez.
The coronavirus pandemic provided a pause in this deadly workplace violence, but the reopening of many companies has brought a return of shootings.More news: Facebook Reverses Course, Won't Ban Lab Virus Theory
It comes just days after an employee at a train yard killed nine people on the other side of the country in California.
Friends and co-workers gathered at a vigil in San Jose on May 27 to mourn those killed in a shooting at a Valley Transportation Authority light-rail facility.
"This type of gun violence has to stop".
Last month, President Joe Biden denounced an "epidemic" that is a source of "embarrassment in the global arena".
And over the past year, gun-related homicides have surged nationwide.More news: Defiant Belarus President Alexander Lukashenko accuses West of waging 'hybrid war'