Tests have found the Zika virus in mosquitoes from Miami, the first detected on continental United States, confirming local transmission of the disease, the Florida authorities said.
Three mosquitoes were taken from the tourist hotspot Miami Beach, where cases of locally transmitted Zika were previously reported.
"This is disappointing but not surprising," Florida agriculture commissioner Adam Putnam said in a statement Thursday.
"Florida is among the best (states) in the nation when it comes to mosquito surveillance and control, and this detection enables us to continue to effectively target our resources," he added.
Health officials reported the first cases of locally transmitted Zika in Miami Beach in mid-August.
The virus, which causes birth defects, was detected in a neighbourhood north of downtown called Wynwood earlier in July. It has also been found in the Florida counties of Palm Beach, north of Miami, and Pinellas, near Tampa.
Zika causes only mild symptoms for most people. But in pregnant women, it can cause microcephaly, a deformation in which babies are born with abnormally small brains and heads.
The disease has also been linked to a potentially fatal disorder known as Guillain-Barre syndrome, which can lead to nervous system problems such as weakness and paralysis.
Zika is spread by mosquitoes and sexual contact.
The authorities have issued an advisory for pregnant women warning of travel to designated active transmission zones in Florida.
The state has so far identified 49 cases of people who contracted the virus locally, the Florida health department says. It reported another 656 cases brought in by people infected while traveling abroad, mainly areas of Latin America where the virus is spreading.
Those numbers include a total of 80 pregnant women affected so far in Florida.