U.S. President Barack Obama on Sunday afternoon called on residents and visitors at East Coast to get prepared for "a serious and big storm" and follow the instructions of state and local authorities as Hurricane Sandy is approaching.

Obama visited the headquarters of the Federal Emergency Management Agency in Washington D.C. on Sunday afternoon to get updated on response efforts for Hurricane Sandy.

After the briefing and a telephone conference with governors and mayors of potentially impacted area, Obama told reporters Hurricane Sandy was "a serious and big storm," urging populations in all the impacted states to "take this seriously."

He called on people to "follow the instructions of your state and local officials because they are going to be providing you with the best advice in terms of how to deal with this storm over the coming days."

Obama also noted that Hurricane Sandy could be unique due to its slow moving. "That means that it may take a long time not only to clear, but also to get, for example, the power companies back in to clear trees and to put things back in place so that folks can start moving back home," he said.

The National Hurricane Center extended its warning on Sunday urging residents of the mid-Atlantic coast to be prepared for life- threatening storm surges.

As of 11 a.m. ET, the storm was about 270 miles (434 km) southeast of Cape Hatteras, North Carolina. Sandy is moving at a speed of 14 miles (23 km) per hour, and is expected to move parallel along the Southeast coast Sunday, approaching the mid- Atlantic coast by Monday night.

Earlier on Sunday, Obama declared a state of emergency for Maryland, making federal aid available for local response.

Several northeastern states, including Maryland, Virginia and New Jersey, have already declared state of emergency by themselves since Friday in preparation for the approaching Hurricane Sandy.

Speaking on CNN's State of Union on Sunday, Virginia Governor Bob McDonnell said the state had learned lessons from the last storm which left many local residents without power for days, and already got about 2,000 additional people this time to help with the state's power supply.

He also said the state Board of Election was already planning for extended hours in advance for absentee voting as the hurricane may potentially prevent voters getting out to cast ballots on Election Day.

The Virginia National Guard was authorized to call up to 300 personnel on state active duty for possible severe weather recovery operations from Hurricane Sandy.

In New Jersey, where Hurricane Sandy most likely makes landfall, Governor Chris Christie ordered a mandatory evacuation of the state's barrier islands, including the casino center Atlantic City, as well as the shutdown of 12 casinos by Sunday afternoon.

New York City also announced the closings of its mass transit and school systems and ordered residents to leave some low-lying areas on Sunday.

Airlines have canceled hundreds of flights into airports along the US east coast ahead of the arrival of a major storm, hundreds of domestic flights have been called off. Some international flights into New York and Washington were also canceled on Monday.

As Sandy approaches, the situation along the East Coast is lining up to repeat the "perfect storm" of 1991, which impacted around Halloween of that year. Just like in 1991, Sandy will meet up with cold front coming out of the Northwest and a high pressure system from Greenland, fueling it with enough energy to make it as powerful as, or even worse than the 1991 storm.

Because it is impacting around the time of Halloween, meteorologists have been using the term "Frankenstorm" to describe the havoc Sandy could wreck for the hundreds of millions of people living along the East Coast.

Obama is balancing between his job and the home stretch of his re-election campaign just nine days before the Election Day. He will travel to Florida later Sunday to prepare for a campaign event Monday.

Sandy has pushed both campaigns of Obama and Republican challenger Mitt Romney to make changes. The Obama campaign canceled Vice President Joe Biden's Saturday rally in coastal Virginia Beach. Some of Obama's planned campaign events in Virginia and Colorado on Monday and Tuesday have also been canceled. Romney also canceled a rally in Virginia and will head to Ohio instead. Endi