CAPE CANAVERAL, Fla. — Hurricane Matthew steamed toward heavily populated Florida with terrifying winds of 130 mph Thursday, and more than 2 million people across the Southeast were warned to flee inland.

The Category 4 is the most powerful storm to threaten the U.S. Atlantic coast in more than a decade.

Matthew left at least 283 dead in Haiti, an Interior Ministry official said. Six other people died in other parts of the Caribbean.

“The storm has already killed people. We should expect the same impact in Florida,” Gov. Rick Scott said.

Matthew was about 75 miles east of West Palm Beach, moving toward the city at 14 mph. As it moved north, it spared 4.4 million people in the Miami and Fort Lauderdale areas from the strongest winds.

“We were lucky this time,” Miami-Dade Mayor Carlos Gimenez said.

Matthew was expected to blow ashore — or come dangerously close to doing so — early Friday north of West Palm Beach, which has about 1.1 million residents, and then push north for the next 12 hours along the Interstate 95 corridor, through Cape Canaveral and Jacksonville, according to the Miami-based National Hurricane Center.

From there, forecasters said it would likely hug the coast of Georgia and South Carolina over the weekend before veering out to sea — perhaps looping back toward Florida next week as a tropical storm.

Millions of people in Florida, Georgia and South Carolina were told to evacuate, and interstates were turned into one-way routes to speed the exodus.

But millions more had hunkered down. Earlier, residents in Florida boarded up their homes and businesses.

“We're not going to take any chances on this one,” said Daniel Myras, who struggled to find enough plywood to protect his restaurant, the Cruisin Cafe, two blocks from the Daytona Beach boardwalk.

“A lot of people here, they laugh, and say they've been through storms before and they're not worried,” he said. “But I think this is the one that's going to give us a wake-up call.”

Forecasters said Matthew could dump up to 15 inches of rain in some spots and cause a storm surge of 9 feet or more.

“A lot of communities are going to be underwater if predictions are correct,” said Colorado State University meteorologist Phil Klotzbach.

President Barack Obama declared a state of emergency for Florida and South Carolina, freeing up federal money and personnel to protect lives and property.

The Pentagon signaled it was preparing for a potentially sprawling effort to assist Americans after Matthew hits, establishing four military bases — Fort Bragg in North Carolina, North Auxiliary Airfield in South Carolina, Marine Corps Logistics Base Albany in Georgia and Fort AP Hill in Virginia — as hubs from which rescue and relief efforts could be staged.

The storm could wallop nearly a dozen military installations up and down the Southeastern coast.

Meanwhile, the Fort Lauderdale airport shut down, and the Orlando airport planned to do so as well. Airlines canceled more than 3,000 flights Thursday and Friday, many of them in or out of Miami and Fort Lauderdale.

Amtrak suspended train service between Miami and New York, and cruise lines rerouted ships to avoid the storm, which in some cases will mean more days at sea.

In west Florida, hotels were filling up.

“My biggest concern is people aren't taking this seriously enough,” Scott said. “I don't want people to lose their life.”

At the Kennedy Space Center in Cape Canaveral, NASA no longer has to worry about rolling shuttles back from the launch pad to the hangar because of hurricanes because the shuttles have been retired. But private spaceflight company SpaceX was concerned about the storm's effect on its leased seaside pad.

The last Category 3 storm or higher to hit the country was Wilma in October 2005. It sliced across Florida with 120 mph winds, killing five and causing $21 billion in damage.

As people hurried to higher ground, authorities in South Carolina said a motorist died Wednesday after being shot by deputies in a gunbattle that erupted when he sped away from a checkpoint along a storm evacuation route.

In Haiti, officials said 283 people died. Many towns were cut off by the storm and the magnitude of the disaster was just beginning to come into focus.

There were four people killed in neighboring Dominican Republic, one in Colombia and one in St. Vincent and the Grenadines.

In the Bahamas, authorities reported extensive flooding but no deaths. The Bahamas National Emergency Management Agency said authorities rescued 30 people who were trapped in their homes on the island of New Providence.

The Washington Post and Miami Herald contributed.