Federal health officials warned pregnant women not to travel to Miami Beach after Florida confirmed that the mosquito-borne Zika virus was active in the popular tourist destination.
The US Centers for Disease Control and Prevention also suggested that pregnant women who are especially worried about exposure to Zika - which has been shown to cause microcephaly - might consider avoiding all of Miami-Dade County.
The new warnings represent a challenge to Florida's multibillion dollar tourism industry, with Miami Beach accounting for nearly half of visitors stays in the city, and heighten concerns over Zika's spread in the continental United States.
In a press conference, Florida Governor Rick Scott said state health officials had identified five cases of Zika believed to be contracted in Miami Beach.
"This means we believe we have a new area where local transmissions are occurring in Miami Beach," he said, noting that the state had already stepped up pesticide spraying efforts in this area.
The new transmissions come as Miami-Dade continues to battle Zika in the Wynwood arts neighborhood of Miami, the site of the first locally transmitted cases of Zika in the continental United States.
In Miami Beach, the state believes Zika transmission is confined to a 1.5-square-mile area located between 8th and 28th streets in the popular South Beach neighborhood, a popular tourist destination. CDC Director Dr Tom Frieden said there have been several cases of Zika believed to have been acquired by local mosquitoes in other parts of Miami that do not yet constitute local transmission.
Given that, Frieden said there could be transmissions that have not been identified throughout Miami, which is why the CDC has advised pregnant women and their sexual partners who are worried about potential exposure to consider avoiding travel to Miami all together.
Of the five new cases in Miami Beach, one person is a resident of New York, one person is a resident of Texas and one person is a resident of Taiwan.
"All three of these people traveled to Miami," Scott said.
Frieden said battling Zika-carrying mosquitoes in this neighborhood will be especially challenging because the area's high rise buildings will prevent pilots from flying low enough to drop pesticides in aerial spraying campaigns.
"The inability to use aerial spraying there means we'll be limited to using ground-based techniques like backpack spraying," he said.
Frieden said aerial spraying continues to be successful in the Wynwood neighborhood, where experts have seen "substantial but not complete knockdowns of mosquito populations.