Irma weakens to category-four storm

Hurricane Irma has been downgraded to a category-four storm but still packs a powerful punch, with winds up to 250km/h as it heads towards Florida.

Hurricane Irma has weakened to a category-four storm on Friday as it batters the Caribbean on a path towards Florida but remains a powerful hurricane.

The US National Hurricane Center says Irma's maximum sustained winds have decreased to near 250km/h. Early on Friday, the hurricane was centred about 90km northwest of Great Inagua Island and 795km southeast of Miami.

The NHC says fluctuations in strength are likely during the next day or two but Irma is expected to stay a category-four storm.