U.S. official says worst of Hurricane Irene over

U.S. Homeland Security Secretary Janet Napolitano said on Sunday that the worst of Hurricane Irene was over but communities still in Irene's path should continue to be vigilant.

Napolitano told a briefing that U.S. President Barack Obama was briefed Sunday morning as Irene was downgraded from a hurricane to a tropical storm.

Irene churned up the U.S. mid-Atlantic coast as category one hurricane since it made landfall in North Carolina Saturday morning. It lost some strength as it hit the New York City Sunday morning, with winds dropping to 65 mph by 9 a.m. EDT, the National Hurricane Center said. Still, Irene remains dangerous as streets at edges of New York City started to flood.

About four million people are currently out of power, as power lines were downed by strong wind and heavy rain and some power plants shut down or reduced operation out of precaution. At least 11 people died from the hurricane in states including North Carolina, Virginia, Maryland and Connecticut.