Hurricane Isaac has come ashore in south-eastern Louisiana in the United States and is heading towards New Orleans.
Isaac is lashing coastal areas with winds of up to 130km/h on Tuesday and is expected to reach New Orleans exactly seven years after it was hit by Hurricane Katrina, which killed more than 1800 people.
The US National Hurricane Center says Isaac is producing a dangerous storm surge along the northern Gulf Coast and flooding from rainfall is to follow.
Massive new floodgates designed to protect New Orleans have been closed on the largest storm surge barrier in the world at Lake Borgne, east of the city.
President Barack Obama has declared an emergency in Louisiana and Mississippi, allowing federal funds to be released to local authorities, the BBC reports.
Power cuts have been reported across low-lying parts of Louisiana and Mississippi, affecting more than 200,000 homes and business.
Mr Obama warned residents in Isaac's path to heed evacuation warnings and not "tempt fate". Thousands of people have fled the area; many of those who stayed behind have locked themselves indoors.
Energy companies have evacuated offshore oil rigs and shut down refineries.
The National Guard has been sent in to help prevent looting in New Orleans, a city of 360,000 people.
Isaac has killed at least 24 people in Haiti and the Dominican Republic, and caused significant flooding and damage in the Caribbean.