A state of emergency has been declared in Louisiana, Mississippi and Alabama as Hurricane Isaac closes in on the US Gulf Coast.

The storm swiped south Florida on Sunday and strengthened over the warm Gulf waters.

Isaac has been raised from a tropical storm to a category one hurricane and is expected to reach land late on Tuesday or early on Wednesday which will be the seventh anniversary of Hurricane Katrina.

The US National Hurricane Center warned the storm could hit towns in at least three US states near the shoreline and flood the northern Gulf Coast with a storm surge of up to 12ft in some areas.

The storm could take direct aim at New Orleans, which is still struggling to fully recover from Katrina, which swept across the city on August 29, 2005, killing more than 1,800 people and causing billions of dollars of damage along the coast.

New Orleans Mayor, Mitch Landrieu, said "That brings a high level of anxiety to the people of New Orleans, I want to tell everybody now that I believe that we will be OK."