Michael has intensified into an extremely dangerous Category 4 hurricane as it howls closer to Florida's Gulf shore with half a million coastal residents urged to seek higher ground.
Michael is projected to plough into Florida's panhandle at midday on Wednesday (3am AEDT Thursday), unleashing potentially devastating waves of seawater as high as four metres that could rush inland for kilometres around the storm's centre, the National Hurricane Centre (NHC) warned.
By Tuesday, Michael was already causing major disruptions to US oil and gas production as it churned north over the Gulf of Mexico.
US President Donald Trump declared a state of emergency for the entire state of Florida, freeing up federal assistance to supplement state and local disaster response.
The latest NHC report said the storm was about 275km from shore and packing sustained winds of up to 210km/h.
Reuters