Tropical storm Irene strengthened into a hurricane today after it began moving across Puerto Rico, bringing torrential rains and winds and threatening to move toward the US later in the week.

More than 1.2 million people in metropolitan New Orleans were warned to get out as 140-mph Hurricane Ivan churned toward the Gulf Coast, threatening to submerge the below-sea-level city in what could be the most disastrous storm to hit in nearly 40 years.