Hurricane Irma is blasting up the West Coast of Florida after buffeting the city of Miami, with dangerous flooding along long stretches of Coast.

It has been downgraded from category three to one but still has maximum sustained winds of 120 kilometres per hour.

More than 3.4 million homes in the state are without power, with parts of the city of Miami under water.

At least four deaths have been linked to the storm and several areas have brought in curfews.

According to National Hurricane center, Irma is expected to weaken into a tropical storm over far Northern Florida or Southern Georgia later on Monday.