After a night of widespread power outages in Florida, Hurricane Matthew pushed slowly northward Friday, prompting officials to extend a hurricane warning into North Carolina and to issue blunt warnings of possible deadly flooding in South Carolina, including the city of Charleston.

"There is nothing safe about what is getting ready to happen," South Carolina governor Nikki Haley said Friday. "This is the last time you will hear my voice when I am asking you to evacuate. We need everybody to consider evacuating and take this very seriously."

South Carolina officials were particularly worried about high water, in the form of 8-foot storm surges, inundating barrier islands and bringing life-threatening flooding to historic Charleston.

Haley said more than 300,000 people have evacuated low-lying areas, but said many people were refusing to leave, particularly on Daniel Island, a 4,000-acre area on the east bank of the Cooper River in the city of Charleston.

As of 11 a.m. ET Friday, the hurricane, downgraded slightly to a Category 3, was located 35 miles east northeast of Daytona Beach, Fla., moving northwest at 12 mph, according to the National Hurricane Center. Matthew continued to pack sustained winds up to 120 mph, threatening devastating storm surges in a four-state area.

As the hurricane trekked northward, the hurricane center extended the hurricane warning as far as Surf City, N.C.

In North Carolina, Gov. Pat McCrory warns of heavy rains at or near the coast and power outages from strong winds. He says the National Guard and emergency equipment, including high-water vehicles and swift-water rescue teams, are being assembled as the storm track closer to the state.

In Georgia, more than 500,000 people fled the coastal areas for the interior and thousands sought refuge at shelters.

Officials in Glynn County, along the coast, warn of widespread devastation on St Simons and Jekyll Islands from what they it call a "1 in 500-year storm surge event" with a 9-foot wall of water carrying 25-foot waves.

“Under the current forecast, total devastation of the barrier islands is possible and portions of F.J. Torras Causeway and Jekyll Island Causeway may be completely lost,” county officials say in a statement.

In Florida, Gov. Rick Scott said at a mid-morning briefing that he remains "very concerned" about the danger of storm surges, and says the "worst effects are sill likely to come."

"The storm has passed only half our state," Scott said at a mid-morning briefing.""So this is not over."

He noted that 600,000 homes were without power and that 22,000 people were being housed in shelters.

In Washington, President Obama said Matthew "is still a really dangerous hurricane" and called on residents of the affected states to "pay attention to what your local officials are telling you."

Officials say people who refused to evacuate from central Florida’s Atlantic coast are calling for help now as Hurricane Matthew’s western eyewall brushes past Cape Canaveral, the Associated Press reported.

More than 100,000 people in the Brevard County area had lost power early Friday, according to emergency operations spokesman David Waters.

Mandatory evacuation orders had been issued for 90,000 people living on barrier islands and in mobile homes and low-lying areas. Waters says some residents who refused to leave now find themselves cut off as they face the worst of the hurricane.

He said a family called in that the roof “just flew off their home on Merritt Island.”

Waters said people will just have to stay put for now and do the best they can until conditions improve and paramedics and firefighters can be dispatched to help them. He spoke by phone from the county’s emergency operations center, which was running a backup generator because it had lost electricity.

Along with the power outages, the water supply to the barrier islands was cut off to avoid compounding the storm flooding if the system got damaged.

Waters said he has talked to other families who have said things like, “We’re scared. We wish we hadn’t stayed.”

Matthew, the most powerful storm to threaten the Atlantic coast in more than a decade left more than 500 dead in its wake, mainly in Haiti, as it roared through theCaribbean, Reuters and the AP reported. Reuters, tallying deaths reported by civil protection officials at a local level, put the toll Friday morning at 572.

The winds picked up along Vero Beach, midway between West Palm Beach and Cape Canaveral, stripping away palm fronds, ripping awnings and blowing sand that stung the face. Waves crashed on the beach, and rain came in short bursts.

As it moved north Thursday evening, Matthew stayed about 100 miles or more off South Florida, sparing the 4.4 million people in the Miami and Fort Lauderdale areas from its most punishing effects.

Forecasters expect Matthew to stick close to the coast of Georgia and South Carolina over the weekend before veering out to sea — perhaps even looping back toward Florida in the middle of next week as a tropical storm.

Fred Johnson, meteorologist at the National Weather Service, said the latest expected path of the hurricane indicates that winds from the storm will be somewhat lower than initially predicted.

Streets in Vero Beach were partially covered with water Thursday night, and hotel guests in Orlando were told to stay inside, though a few sneaked out to smoke or watch the rain.

In Washington, 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.