(Miami) (AP) — Residents in parts of the Miami metro area are under mandatory orders to leave their homes as Hurricane Irma barrels toward South Florida with potentially catastrophic winds.

Mayors in Miami-Dade and Broward counties issued mandatory evacuation orders starting Thursday morning for barrier islands and low-lying mainland areas in the metro area of 6 million, where forecasters predict the hurricane with winds of 180 mph could strike by early Sunday.

Florida Gov. Rick Scott strongly urges people to evacuate if asked to do so by local officials. The governor also says he expects the state’s gas stations to have fuel Thursday, after talking with fuel retailers a day earlier.

Hurricane Irma is hitting Puerto Rico with heavy rain and powerful winds, and more than 900,000 people are without power. Authorities in the Caribbean are struggling to get aid to small islands already pounded by the historic storm earlier Wednesday. Antigua and Barbuda Prime Minister Gaston Browne said Wednesday nearly every building on Barbuda was damaged when Irma passed overhead and about 60 percent of the island’s roughly 1,400 people are homeless.