Emergency management officials across South Florida are hastening disaster preparations in anticipation of Hurricane Irma's expected weekend arrival on the US mainland with possibly greater force than Hurricane Harvey unleashed on Texas, Reuters has reported.

Irma is currently a Category 5 storm, the highest hurricane ranking used by US forecasters, and was approaching the Caribbean's northern Leeward Islands, east of Puerto Rico, late last night with maximum sustained winds of 185 miles per hour, or 300 km/h.

The US National Hurricane Centre in Miami forecast that the storm would make landfall in Florida on Saturday, although Irma's precise trajectory remained to be seen.

Forecasters described the storm as "potentially catastrophic." Irma ranks as one of the five most powerful Atlantic hurricanes of the past 80 years and is the strongest Atlantic storm ever recorded outside the Caribbean Sea and Gulf of Mexico, added Reuters.