Officials across the north-eastern Caribbean have cancelled flights, closed schools and urged people to shelter indoors as Hurricane Irma barrels towards the region after strengthening to a Category 5 storm.

The US National Hurricane Centre said the “potentially catastrophic” storm is the most powerful seen in the Atlantic in more than a decade.

Irma has maximum sustained winds of 180mph as it bears down on the twin-island nation of Antigua and Barbuda.

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It was centred about 225 miles east of Antigua in the late morning and moving west at 14mph.

The centre said there is a growing possibility that the storm’s effects could be felt in Florida later this week: “Everyone in hurricane-prone areas should ensure that they have their hurricane plan in place.”

Irma’s centre is expected to move over portions of the northern Leeward Islands late on Tuesday and early on Wednesday, the hurricane centre said.

The eye is then expected to pass about 50 miles from Puerto Rico late on Wednesday.

Irma is the strongest Atlantic hurricane since Rita in 2005, officials said.

“Puerto Rico has not seen a hurricane of this magnitude in almost 100 years,” said Carlos Anselmi, a National Weather Service meteorologist in San Juan.

Authorities warned that the storm could dump up to 12in of rain, cause landslides and flash floods and generate waves of up to 23ft.

Government officials began evacuations and urged people to finalise all preparations as shelves emptied across the region.

“The decisions that we make in the next couple of hours can make the difference between life and death,” Puerto Rico governor Ricardo Rossello said. “This is an extremely dangerous storm.”

(AP)(AP)

Hurricane warnings were issued for 12 Caribbean island groups including Antigua and Barbuda.

Prime minister Gaston Browne said was confident Barbuda would weather the storm because its shelter was built with reinforced concrete and equipped with a back-up generator.

“I am satisfied that at a governmental level that we have done everything that is humanly possible to mitigate against the effects or the potential effects of this storm,” he said.

“What is really required now is for Antiguans and Barbudans … to follow the warnings and to act appropriately so that we do not end up with any serious casualties or any fatalities.”

Antigua’s airport announced it was closing with an ominous statement advising visitors and residents to protect themselves from the “onslaught” of the storm: “May God protect us all.”

Puerto Ricans braced for blackouts after the director of the island’s power company told reporters that storm damage could leave some areas without electricity for four to six months.

The utility’s infrastructure has deteriorated greatly during a decade-long recession, and Puerto Ricans experienced an island-wide outage last year.