Irma, a category 5 hurricane, has made landfall with maximum sustained winds of 160 mph after causing widespread devastation in the Caribbean islands, the US National Hurricane Centre (NHC) said.
According to the NHC, Irma hit the island nation's Camaguey archipelago at 11 pm on Friday night, reports CNN.
Cuban authorities have evacuated some 700,000 civilians so far.
NHC forecasters said the storm's wind speeds will increase after Irma passes Cuba then slips into the extremely warm waters near the Keys.
Irma is expected to have sustained winds of 160 mph by the time it slams into the Florida Keys on Sunday.
"Nowhere in the Florida Keys will be safe," the National Weather Service tweeted.
Many Florida counties are under evacuation orders.
"If you have been ordered to evacuate, leave now. Not tonight, not in an hour, now," Governor Rick Scott said on Friday night.
"Staying in homes could subject residents to storm surge as high as 12 feet."
At least 24 people were killed this week when Irma pummelled northern Caribbean islands such as Barbuda and the Virgin Islands.
In Puerto Rico, hundreds of thousands of people―nearly 70 per cent of the US territory's utility customers―were left without power, reports CNN.
Irma slammed the Turks and Caicos and southeastern Bahamas earlier on Friday before it was off to pound northern Cuba and the central Bahamas.
When it first made landfall, Irma sustained maximum wind speeds of at least 185 mph for at least 37 hours, longer than any storm on record.
The Red Cross estimates 1.2 million people have already been battered by the storm.
