Maryland Gov. Martin O’Malley (D) on Sunday warned state residents to “be vigilant and be prepared” as Hurricane Sandy begins to arrive and to evacuate low-lying or flood-prone areas.

Ocean City is already under a mandatory evacuation order.

“This is serious, killer storm,” O’Malley said. “This story has already killed a number of people in the Caribbean and will likely take more lives as the storm hits the mid-Atlantic and the Eastern U.S.”

He said he expected many in the state would suffer power outages that could last for days.

O’Malley said that 450 National Guard troops have been mobilized and are ready to respond with 400 Humvees, utility vehicles and generators.

O’Malley said Marylanders heading to the polls for early voting Sunday will be able to vote until 6 p.m., but early voting would be cancelled Monday. It will likely be rescheduled for Friday, O’Malley said.

Several Maryland schools have already announced they would be closing Monday, including Howard County. Prince George’s County Schools are already slated to be closed for an administrative day, O’Malley said.

O’Malley said that the state would experience intense wind, rain and that coastal areas would see waves not seen since Hurricane Gloria in 1985.

“This storm is very intense with very severe winds over a wide area that will last a long time and for a prolonged period.” O’Malley said. “Everybody needs to take precautions.”