Utility crews were working feverishly to restore power to hundreds of thousands of homes and businesses in the eastern US after an ice storm knocked out electricity to more than a million customers, damage one official likened to that from a hurricane.

America’s worst blackout should have been contained by operators at Ohio’s FirstEnergy firm, a three-month US and Canadian investigation has concluded.

The Ohio power company under the spotlight following the biggest blackout in America’s history has said there were problems, including strange voltage fluctuations, in the Midwest power grid hours before its transmission lines failed.

A woman alerted power company staff after she received an unusually high bill - only to discover her electricity was allegedly powering heat lamps for her neighbours’ homegrown marijuana, police said today.