Irma is expected to remain a powerful hurricane for at least five days. It is currently at the Leeward Islands (which include Antigua, Barbuda and Sint Maarten), and is forecast to churn its way over Puerto Rico, the Dominican Republic, Haiti and Cuba to reach Florida.
The USNHC called Irma a "potentially catastrophic category 5 hurricane" that would bring "life-threatening wind, storm surge, and rainfall hazards".
There's little news from the Caribbean islands affected so far as large swathes have no power, although there have been some reports of property damage.
Antigua and Barbuda Prime Minister Gaston Browne tweeted that the islands had been spared the worst of the storm.
The MFAT website says New Zealanders in Irma's path should follow the advice of local authorities and seek shelter.
"It is generally considered sensible practice not to venture outdoors and remain well away from the sea."
New Zealanders can register and update their travel plans on the New Zealand government SafeTravel website.
New Zealanders who need urgent consular assistance can contact the New Zealand High Commission in Barbados on +12466227800 or after hours on +12462317356.