Obama: 'We have to be prepared for the worst'

President Barack Obama has warned Hurricane Irene, currently looming off the east coast of the US, could be a "historic" storm.

Seven states from North Carolina to Connecticut have declared emergencies ahead of Irene's arrival on Saturday.

Mandatory evacuations have been ordered in parts of four states.

President Obama warned people to "be prepared for the worst... if you're in the way of this hurricane you should be preparing now".