Arek Sarkissian, J.D. Gallop and Doug Stanglin

USA TODAY NETWORK

MELBOURNE, Fla. — Hurricane Matthew strengthened to an "extremely dangerous" Category 4 storm and began hitting Florida Thursday afternoon in an expected 500-mile trek of life-threatening winds and storm surges from West Palm Beach to South Carolina.

With Florida, Georgia, South Carolina and North Carolina under states of emergency, Florida Gov. Rick Scott issued a blunt warning to his 1.5 million coastal residents: "This storm will kill you."

In Washington, President Obama declared a state of emergency in more than two dozens Florida counties as the potentially catastrophic storm approached.

The directive authorizes the Department of Homeland Security and the Federal Emergency Management Agency to coordinate efforts to alleviate suffering caused by the hurricane.

The Department of Defense also stepped in and approved a request by the United States Agency for International Development to unlock $11 million in humanitarian and civic disaster aid in response to the hurricane, Pentagon press secretary Peter Cook told reporters Thursday. The U.S. Southern Command is overseeing U.S. military relief efforts in Haiti and a team arrived in Haiti Wednesday, Cook said.

The U.S. Northern Command has designated sites in or near Charleston, S.C., Albany, Ga., Fort Bragg, N.C., and Fort A.P. Hill, Va., as bases of operation for the Federal Emergency Management Agency, according to Cook.

FEMA administrator Craig Fugate issued a statement Thursday imploring the public to follow evacuation orers and assuring them that FEMA was ready to meet their emergency needs.

"We have not seen a hurricane this strong in almost a decade," he said. "If instructed to evacuate, don't wait. You can always repair and rebuild -- and we'll be here to help you do that. The most important thing you can do is keep you and your family safe."

While the storm's exact track could vary slightly as it locks into its final path in the sweep up from the Caribbean and out of the Bahamas, Scott said Florida "must prepare for a direct hit."

Forecasters say Miami and Fort Lauderdale, the state's most densely populated areas with over 4 million people, would likely escape the worst winds, but would still face tropical-storm force winds of between 39 mph and 73 mph.

West Palm Beach and the Cape Canaveral areas, home to NASA's Kennedy Space Center, however, were bracing for the main force of the storm beginning around midnight as it rolled northward.

In Haiti, officials dramatically increased the death toll Thursday night in that country to 283. At least four died in the Dominican Republic, Haiti's neighbor on the island of Hispaniola. Deaths also were reported in Colombia and St. Vincent and the Grenadines.

“The storm has already killed people. We should expect the same impact in Florida,” said Scott Thursday afternoon as Matthew’s outer bands of rain appeared.

The governor's message was clear: "Evacuate, evacuate, evacuate. Time is running out. We don't have much time left."

As of 5 p.m., ET Thursday, Matthew had intensified to a Category 4 storm, with sustained winds ranging from 130 mph to 156 mph, according to the U.S. National Hurricane Center (NHC).

The strong winds not only threaten to knock down trees, shatter windows and rip roofs from houses, but also churn up dangerous storm surges as high as 11 feet — at high tide —along the Florida coast. Forecasters say some areas could be drenched by up to 15 inches of rain.

The storm was centered about 100 miles east southeast of West Palm Beach, Florida, and moving northwest toward the state at 13 mph, according to the NHC.

Matthew is expected to hit the mainland at full force as early as midnight Thursday.

The storm was expected to race up the coast this weekend as far as South Carolina then, in an odd twist, some long-range forecast models show Matthew potentially looping back around toward Florida next week, potentially striking the state a second time.

More hurricane coverage:

• Hurricane Matthew will hit today: Here's what we know

• See every storm path in Florida for the past 100 years

• Here's why South Carolina is better prepared for Matthew than it was for Hugo

• Airline cancellations soar to 2,700 through Friday

• 'These guys are crazy,' People hit the beach ahead of the storm

• Which 'spaghetti model' is best to gauge hurricanes

• A link to full coverage of Hurricane Matthew

In order to spur evacuation routes, Scott has canceled tolls in the affected areas, including the entire Florida Turnpike, Alligator Alley, Central Florida Expressway Authority and the Miami-Dade Expressway Authority, to help speed evacuation.

He said the National Guard deployment had been beefed up 2,500 and another 4,000 were on call for help with late evacuations and shelters. Scott said hospitals along the coasts were already being evacuated.

Before 2 p.m. Eastern time, flight-tracking service FlightAware.com reported that 1,500 Thursday flights within the U.S. had been scrapped, with the largest numbers at Fort Lauderdale and Miami. American Airlines, which has a major hub in Miami, was the hardest-hit carrier, followed by Southwest Airlines and JetBlue Airways.

FlightAware said airlines had already canceled 1,300 more flights scheduled for Friday. Delta Air Lines said cancellations were likely to spread to coastal Georgia and South Carolina on Saturday, the Associated Press reports.

In Orlando, Walt Disney World was closing all of its theme parks in the area.

In historic Savannah, Ga., a city of handsome antebellum mansions that hasn’t taken a direct hit from a major hurricane since 1898, many people heeded the order to leave.

“Hurricane Matthew is a storm not to be messed with,” Savannah Mayor Eddie DeLoach said. “If you decide to ride it out, do not expect us to be there to help you.”

Near Savannah, outside of the Tybee Time Bar on Tybee Island, bartender Brian Herfurt served beers to a group of neighbors who said they will stay for the duration in their apartment steps from the beach.

Their biggest concern, says Clint Troop, who has lived on Tybee for eight years, isn’t being able to leave the island – it’s getting back on.

“We don’t want to sit on I-16 or I-95 for eight hours and only go a mile and then not be able to come back home,” he says.

Steve Smith, drinking alongside and also planning to stay, said he has lived through the threat of storms for the 20 years he’s lived on Tybee. But this time, he said, he believes the storm will heavily impact the barrier island and inland historic Savannah.

“It’s going to do what it’s going to do,” Smith says. “I know it’s coming here, I don’t know hard.”

Rockledge and east Viera, Fla., looked like ghost towns by noon Thursday.

The construction signs and equipment that have cluttered Barnes Boulevard in Rockledge for months were almost all cleared as rain pelted the nearly empty roadway. Stores such as Publix and Walgreens remained open for only a few hours this morning, shutting their doors by noon. Only a Wendy’s remained operating as the day moved on, a line snaking around the drive-through about 3 p.m. Birds chirped as rain fell and the distant hum of power saws filled the air in subdivisions such as Chelsea Park.

Along the southeast coast, many motorists jammed highways. But still others took their departure in stride.

Along A1A Highway, Paul MacDonald took one last walk with his wife and daughter before they closed up their house on Delray Beach to ride out the storm.

While the storm clouds looked ominous and the forecast called for widespread destruction along their beloved coastline, the Detroit native said it could be worse. "It still beats the snow," he said.

In Broward County, as Matthew closed in, a steady stream of shelter seekers walked in to the Atlantic Technical College Arthur Ashe Jr. campus. They carried bags of groceries, cases of water, blankets and pillows. Emergency management officials counted more than 1,400 people staying in 10 shelters as of Thursday morning. Broward County is under a hurricane warning.

“It’s going to be a long day,” said Doug Gordon, 60, a Port Everglades welder who decided it was too dangerous to ride out Matthew in the trailer where he is staying in Dania Beach.

Lynne Larkin, of Vero Beach, says she stayed put through three previous hurricanes, but the approach of a Category 4 Matthew pushed her — and her cat, Ginger Baker — to evacuate her condo this time.

"It's a dilemma because it's a great bunker now full of bottled water, gas grill, ice, food, etc. But everyone is trying to scare me to move inland where there is more flooding threat, and even shelters aren't any sturdier than my home. Suffer in town, suffer at home?"

The governors of South Carolina and North Carolina have also declared states of emergency along the coast in anticipation of high-winds and life-threatening storm surges as high as 9 feet in some areas. In Charleston, city officials say the city has run out of sandbags after distributing 15,000 — more than for any other storm.

South Carolina Gov. Nikki Haley urged residents to get at least 100 miles from the shore, reminding residents who've decided to stay that they could be putting the lives of law enforcement and emergency responders in danger, not just their own.

Roughly 250,000 residents and tourists fled South Carolina's Lowcountry by Wednesday evening ahead of the approaching storm. At least as many more are expected to evacuate Thursday.

Authorities say a motorist in South Carolina was shot and wounded by deputies during an altercation over a Hurricane Matthew evacuation route, the Associated Press reported.

Berkeley County Sheriff Duane Lewis said a motorist knocked down some traffic cones at a check point in Moncks Corner and sped off.

The sheriff said when deputies finally caught up with the driver a few miles away he pointed a gun at deputies and started shooting. The sheriff said the deputies shot back, wounding the man who was taken to the hospital. His name and condition were not immediately released. No deputies were wounded.

Gallop reporting for Florida Today, Arek Sarkissian reporting from Tallahassee for The Naples Daily News; Stanglin reporting from McLean, Va. Contributing: Alan Gomez in Miami, Jane Onyanga-Omara in London, Elizabeth LaFleur in Greenville, S.C. and John Bacon in McLean, Va., Sara Pauson, Florida Today, Eric Connor, Greenville News.