A cluster of Zika cases most likely transmitted by local mosquitoes has been identified in Miami Beach, a health official said Thursday. Health authorities are trying to decide whether to designate a section of the bustling tourist city as a zone of active Zika transmission, and whether to advise pregnant women to avoid the area.

The health official said Thursday that there are “a handful of cases” of likely local transmission that involve people who were in “close proximity to each other.” The official insisted on anonymity, saying that the cases and the location are not likely to be officially announced until late Thursday or early Friday.

Neither the Centers for Disease Control and Prevention nor the Florida Department of Health had released official information on the cases or the location in Miami Beach.

To date, only one neighborhood in Miami, a one-square mile section of Wynwood, has been declared an active Zika transmission zone in the United States, and the C.D.C. has advised pregnant women to stay out of the area. As of Wednesday, Florida authorities had tied 25 of the 35 locally-transmitted Zika cases to a single area in that Wynwood zone.