Public Health England is advising pregnant women to consider postponing any non-essential trips to Florida, amid concerns over the Zika virus.
Its travel advice was updated after the US state confirmed that four people in Miami with the Zika virus appear to have been infected by local mosquitoes.
Previous US cases have been connected to people who caught the virus abroad.
Zika causes only a mild illness in most people but the virus has been linked to severe brain defects in newborns.
More than 1,650 cases of Zika have so far been detected in the United States, but the Florida cases would be the first in the US not involving sexual contact or foreign travel.
The US Centre for Disease Control does not expect a widespread outbreak but says it is preparing for small clusters of infections across the country.
Meanwhile, Florida has announced more aggressive mosquito-control efforts and politicians are keen to assure tourists the state is safe to visit.
The advice from Public Health England is based on a list of countries and territories with current active Zika virus transmission as classified by the European Centre for Disease Control.
Florida is listed as having a moderate risk rating for the Zika virus, along with Guinea-Bissau, Indonesia and the Philippines.
Many more areas, including a number of countries in south and central America and the Caribbean, are categorised as being high risk, where the advice is for pregnant women to postpone non-essential travel, rather than just considering postponing.
Links to Public Health England’s advice on Zika are also provided on the websites of Public Health Wales and Northern Ireland’s Public Health Agency.
Health Protection Scotland provides similar advice on its website, although the section on the Zika virus is yet to include information about the situation in Florida.