Weather forecasters say Hurricane Irene continues to hit parts of the U. S. east coast with heavy rains and strong winds, after claiming the lives of at least four people.

U.S. officials say three people were killed in North Carolina and one in Virginia.

Irene blasted ashore in the eastern state of North Carolina early Saturday, flooding streets and toppling trees with sustained winds of 140 kilometer per hour. More than 630,000 homes and businesses are without power.

The U.S. National Hurricane Center said the massive storm system is expected to continue moving north-northeast at about 24 kilometers per hour. Forecasters warned the category One storm would pass through the Washington D. C. area during the evening and overnight hours without losing strength.

Earlier Saturday, U.S. President Barack Obama visited the command center where senior emergency officials have been coordinating the country's response. He warned the situation would be “touch and go” for the next 72 hours.

U.S. Homeland Security Secretary Janet Napolitano warned residents in the projected path of the storm to take all warnings seriously, saying anyone in an area asked to evacuate needs to leave. She added that anyone not asked to evacuate should “hunker down” .

Forecasters say hurricane-force winds are being felt up to 150 kilometers away from the eye of the storm. They said there is also a danger of tornados forming along the outer edge of the storm.

Forecasters say Irene's projected path is still expected to take it through some of the country's most densely populated areas, including Washington, Philadelphia, New York and Boston.

In New York, Mayor Michael Bloomberg has ordered the city's first ever mandatory evacuation. Some quarter-million people have been told to leave their homes in low-lying areas of the city, including the Wall Street financial district. And in another first, New York's entire public transit system, including subway trains and buses, shut down at midday, as well as all three of New York's major airports.

Airlines have already canceled hundreds of flights elsewhere on the east coast, and train service in parts of the eastern region have been suspended.

The Red Cross said its response to Irene could be one of the largest it has undertaken in recent memory. The organization is responding to more than a dozen states, and says it could take week, even months, to be able to fully address the disaster.

Irene is the first hurricane to seriously threaten the United States in three years. Besides the U.S. fatalities, Irene has killed at least one person in Puerto Rico and two in the Dominican Republic, and destroyed homes in The Bahamas.

Irene also hits at the six-year anniversary of Hurricane Katrina, whose flooding killed more than 1,800 people and forced more than a million residents from their homes in the southeastern United States. The federal response to that disaster was widely criticized as slow and mismanaged, and U.S. officials are determined to be prepared this time.