The ambulance driver who took John Travolta's late son to hospital following his fatal seizure has been formally charged for his part in an alleged plot to extort money from the movie star.

A hurricane watch has been posted in North and South Carolina ahead of Tropical Storm Hanna, which is now passing near the Bahamas.

Tropical Storm Hanna knocked out power to the southern Bahamas and authorities from Nassau to South Carolina warned residents to prepare for evacuation as it moved north, growing into a hurricane.