At least four people were killed on Saturday after Hurricane Isaias made landfall near Destin in the US state of Florida as a dangerous Category 2 storm, before weakening into a post-tropical cyclone, according to local authorities.

The victims included two people killed by falling trees in Florida and Alabama, officials said.

Nearly 670,000 customers remained without power in Florida, Alabama, Georgia and Mississippi as of midday Saturday, according to data from utility tracker PowerOutage.us.

Isaias is forecast to continue weakening as it moves inland this weekend. However, hazardous conditions are expected to persist, with storm surges, flash flooding, damaging winds and a risk of tornadoes across parts of the US Southeast, the National Hurricane Center (NHC) said.

Recovery efforts have begun along the Gulf Coast as Isaias has caused damage across several states.

Businesses, roads and airports are reopening in areas affected by the storm, but further flooding could occur over the next couple of days, Florida officials said at a press conference on Saturday afternoon. Downed trees and debris continue to contribute to widespread power outages in the region.