This came as Florida Gov. Rick Scott announced the confirmation of five cases of Zika transmitted by mosquitoes in Miami Beach.

The Centers for Disease Control and Prevention quickly issued a second travel advisory Friday afternoon, saying pregnant women should also avoid the designated area of Miami Beach.

"They were bitten by mosquitoes from this area", said Center for Disease Control Director Dr. Tom Frieden.

Travel expert Henry Harteveldt, founder of travel consultancy Atmosphere Research Group, said the Zika outbreak in South Florida could jeopardise travel in the area.

Senator Harry Reid, the Democratic minority leader, said the transmission of Zika in Miami Beach "is the most alarming development yet in the rapidly growing threat of Zika in the United States". Officials said five people, including travelers from New York, Texas and Taiwan, had been infected there. This new location is 1.5 square miles from 8th Street to 28th Street between the beach and the intracoastal.

Florida's Department of Health said there are 35 cases of likely local transmission in the state, including the two new cases that were identified Thursday outside of the Wynwood neighborhood.

Officials continue to struggle with controlling mosquitos in the Wynwood area of Miami, Frieden said. Zika virus infection during pregnancy can cause microcephaly and other severe fetal brain defects. But the virus only causes mild, flu-like symptoms in most people, making it hard to confirm local transmissions, the CDC said.

Pregnant women and their partners living in or who must travel to the designated areas should be aware of active Zika virus transmission and take necessary steps to prevent mosquito bites.

He cited congenital syphilis ― when a pregnant woman infected with the disease passes it to her child ― as a more common STI, with equally grave consequences.

In addition to mosquitoes, the Zika virus can be transmitted through sex. Women who want to get pregnant, along with their partners, are urged to use mosquito spray and condoms or avoid sex altogether.

Reporting Aug. 17 in the New England Journal of Medicine, doctors believe that a blood donor passed along the typically mosquito-borne virus in late January to two hospitalized patients who needed transfusions.

Scott said that the virus can also be spread if a mosquito bites the infected person, then bites someone else during the virus' incubation period, which is anywhere from onset to 10-12 days. The Ventura County case is the 171st diagnosed in California, according to state health officials. In Florida's Broward County, which is adjacent to Miami-Dade County, where active Zika transmissions are occurring, abstinence-only rhetoric is trumping public safety ― at least for now. The first large outbreak of disease caused by Zika infection was reported from the Island of Yap (Federated States of Micronesia) in 2007.

William Talbert, president of the Greater Miami Convention and Visitors Bureau, said hotels experienced minor cancellations after the first Zika cases were announced in Wynwood.

Asked by a reporter about the speed of Scott's announcement, Frieden praised Florida's "aggressive" actions, saying the process of identifying and tracing local spread of Zika is "complex".

No cases of Zika virus connected to local mosquitos have been reported in Pinellas County.