The five native cases of Zika contagion in Miami Beach occurred, according to the Florida Health Department, in a very small area of just 1 1/2 miles (2.4 kilometers) in diameter, Efe news reported.
In Miami Beach, officials say, Zika transmission is confined to a 1.5sq mile area located between 8th and 28th streets in the popular South Beach neighbourhood.
None of the people infected in Miami Beach have traveled to Zika-infected regions, which suggests that mosquitos in the area of Miami Beach are infected and spreading the virus.
Earlier this week, U.S. health officials declared a public health state of emergency in Puerto Rico where the number of Zika virus infections have doubled to more than 10,000 in the past three months. In addition, women and men who have traveled to the area should wait at least eight weeks to try to get pregnant even if they didn't catch Zika during their visit.
CDC officials did not immediately respond Friday to questions about whether their travel advisory, the agency's first for pregnant women within the continental US, would be expanded.
CDC Director Tom Frieden said, "We're in the midst of mosquito season and expect more Zika infections in the days and months to come".
The US Centers for Disease Control and Prevention referred calls to state health officials.
So far, Florida is the only state in the mainland USA where it has been reported.
The five cases in Miami Beach involve two local residents and three tourists - hailing from New York, Texas and Taiwan - Florida Governor Rick Scott told a news conference.
But Scott, speaking at the Miami-Dade Department of Health, said the state needs more federal help: An additional 5,000 Zika antibody test kits to ensure rapid testing, additional lab support and personnel, and 10,000 Zika prevention kits for pregnant women.
The CDC said the first Miami Beach case was identified in late July.
Scott asked for perspective Friday, noting that there are 36 locally transmitted cases of the virus and 20.6 million people living in the state.
The escalation of the Zika crisis here sent tremors through the tourism industry and stoked the fears of pregnant women, anxious about the virus' ability to cause severe brain damage in infants.
The CDC previously warned pregnant women to avoid the Wynwood arts district in Miami. However, the warnings also tend to heighten concern generally about the spread of the Zika virus in the continental United States.
So far, Florida is the only state in the mainland U.S. where it has been reported. Containment there will be hard because high-rise buildings and strong winds make it impractical to spray the neighborhood from the air, officials said Friday.