U.S. President Barack Obama said on Sunday that Irene, which had been downgraded to tropical storm status from category one hurricane, remains "a dangerous storm" as the public is still at risk of flooding and power outages.

US President Barack Obama speaks about damage done by Hurricane Irene next to Homeland Security Secretary Janet Napolitano (C) and Federal Emergency Management Agency Administrator Craig Fugate (R) in the Rose Garden of the White House in Washington, August 28, 2011. [China Daily]

Speaking in a White House address, Obama said that the federal government remains concerned about localized flooding.

"This is not over," he said, urging the public to continue to follow the directions of state and local officials.

"The impacts of this storm will be felt for some time. And the recovery effort will last for weeks or longer," said Obama. He pledged that federal agencies will "do everything in their power" to help those affected communities to recover.

While delivering the short statement, the president was flanked by Homeland Security Secretary Janet Napolitano and Federal Emergency Management Agency (FEMA) Administrator Craig Fugate.

"We urged all Americans to take prudent steps to stay safe," said Napolitano.

Waves break along the pier which was damaged during Hurricane Irene, in Ocean City, Maryland August 28, 2011. [China Daily]

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. and was thus downgraded to tropical storm status, according to the National Hurricane Center. As it moved up into New England region, the storm lost steam even further, though still brought strong winds and heavy rains.

At least 15 people died from the storm across six states, and more than four million people were knocked out of power.

"Power could be out for days," the president warned, asking people to be patient as "response and recovery efforts will be an ongoing operation."

Obama cut short his vacation in Martha's Vineyard, Massachusetts, to return to the capital city of Washington ahead of the storm's arrival. He had warned that the hurricane could be "historic" and urged people to "take it seriously."