Washington:  Some 6,500 US troops are being mobilised to conduct disaster relief and rescue missions in the country's east coast endangered by hurricane Irene, Xinhua reported.

Defence Secretary Leon Panetta issued the order for troops from all branches of the US military to support disaster relief if the affected states calls for help, George Little, the spokesman of the defence department, said.

Earlier on Friday, Panetta directed the US Northern Command to provide support as identified by Federal Emergency Management Agency (FEMA).

The Pentagon also propositioned 225 trucks loaded with equipment, food, water and generators at Fort Bragg Base in North Carolina.

In addition, 18 military helicopters have been deployed to the eastern coastal states for life-saving and life sustaining support. Approximately 101,000 National Guard troops were mobilized to provide disaster relief and rescue missions to the possibly affected areas if needed.

Bracing for the worst scenario as hurricane Irene started pounding the US mainland on Saturday morning, at least 10 states along the US East Coast have declared state of emergency, which means that they can get relief aid from the federal government if the storm causes severe damages.

The warnings about possible widespread destruction by the hurricane have triggered evacuation of over two million people in the coastal states along the US East Coast, from North Carolina in the south to Maine in the north.

Irene was expected to cause widespread flooding, power outages and tornadoes, even as it was downgraded Saturday morning from Category 2 to Category 1, with weakened force. 

US government officials warned Saturday that Irene, although a little weakened after it slammed the shores of North Carolina, remained 'dangerous' and residents on the East Coast have to take it seriously and get prepared.

The warning was issued at a joint press conference held by Secretary of the Homeland Security Department Janet Napolitano, FEMA Administrator Craig Fugate and National Hurricane Centre Director Bill Read.

Napolitano said Irene remained a 'large and dangerous' storm as it was advancing up the East Coast, and the residents living on the projected path of the storm have to get prepared by abiding evacuation orders or stocking up on drinking water, food, flashlights and other emergency supplies.

Read said he expected that the beach resorts along the coast of New Jersey to be affected by the storm Sunday morning and a storm surge was forecast for Long Island Sound and New York City. 

The public transit systems in New York City were closed as of noon Saturday for precautions, as city authorities had ordered the mandatory evacuation of about 300,000 people living in low-lying and coastal areas.

Irene has already demonstrated its destructive force after making its landfall in North Carolina Saturday morning, bringing about high wind, torrential rain, flooded streets and power outages.

About 200,000 North Carolina customers of Progress Energy were reported to be living in dark as the storm knocked out the power Saturday morning.

A man was killed in a rural area of Nash County, North Carolina, when he was hit by a tree branch while walking outside his home, becoming the first victim of Irene.

Another man in Onslow County died from heart attack while putting up plywood board to the windows of his house to shield it from the storm, according to the North Carolina Emergency Management Agency.