Florida's emergency management division says nearly 6,000 people are already huddling in shelters ahead of Hurricane Irma.
Most of the evacuees are gathered in shelters in Broward and Miami-Dade counties, where catastrophic Category 4 winds are expected to hit this weekend.
Hundreds of thousands of residents have fled in anticipation of Irma's winds and storm surge, which have already killed at least 20 people in the Caribbean.
Many roads leaving the state have been jammed with traffic.
Gov. Rick Scott has directed all public schools, colleges and universities and state offices to close through Monday at least to make them available for shelter and staging of recovery efforts.