MIAMI BEACH — A cluster of Zika cases most likely transmitted by local mosquitoes has been identified in Miami Beach, and federal and state officials are considering whether to advise pregnant women to avoid traveling to the city and possibly even all of Miami-Dade County, a health official said Thursday.

Such a decision would signal that the potential threat of local Zika transmission had catapulted to a new level. It would no longer be confined to one zone of active local transmission in Miami — the only one identified in the continental United States up to now. A broad travel advisory could threaten tourism in South Florida and deepen fears among pregnant women living in the area.

The Miami Beach City Manager Jimmy Morales, in an email to city commissioners, confirmed that two cases of Zika have been tied to Miami Beach. One case is a tourist who had visited Miami Beach two weeks ago. Another case involves a Miami Beach resident who works on the island, Mr. Morales said in the email, which was first reported by The Miami Herald.

“I have been informed that two Zika cases have been linked to Miami Beach,” Mr. Morales said in the email.