CHARLESTON, SC --Hurricane Matthew made landfall as a minimal Category 1 hurricane at around 11am EST in McClellanville, South Carolina.
Officials say winds remain at 75 miles per hour as Matthew moves to the northeast.
The expectation is for Matthew to weaken to a tropical storm by this evening, but emergency officials say the warnings have not changed.
Torrential rains are expected to bring significant flash flooding to parts of North and South Carolina throughout the day, with several more inches of rain expected in northeastern South Carolina this evening. As much as 10 to 12 inches is forecast for areas across the coast as the storm moves through over the next 24 hours.
PHOTOS: The wrath of Hurricane Matthew in pictures
The threat for isolated tornadoes is also a significant risk from Myrtle Beach, South Carolina through the areas surrounding Wilmington and New Bern, North Carolina.
Some of the South's most historic cities faced the weakening but still powerful Hurricane Matthew as it plowed north along the Atlantic coast, flooding towns and gouging out roads in its path.
The storm killed at least four people in Florida and knocked out power to more than 1 million homes and businesses, even though its strongest winds stayed just offshore.
Matthew was making itself felt in South Carolina Saturday morning. Hurricane-force winds were moving onshore at Hilton Head and Pritchards Island, South Carolina, the National Hurricane Center reported. At least one wind gust of 61 mph (98 kph) was recorded at Beaufort, South Carolina.
More than 150,000 electric customers in South Carolina - most in Beaufort and the Charleston area - were without power Saturday morning.
The Category 1 hurricane will near North Carolina's southern coast by Saturday night, the center says.
"Now is the time we ask for prayer," Gov. Nikki Haley said as she finished an update on storm preparations and bowed her head.
Matthew - the most powerful hurricane to threaten the Atlantic Seaboard in more than a decade - set off alarms as it closed in on the U.S., having left at least 300 people dead in Haiti.
In the end, it brushed the heavily populated areas of Florida and raked the Georgia coast, including some of the state's islands such as St. Simons and Tybee.
Steve Todd defied orders to evacuate Tybee even after the mayor called and pleaded with him to leave. As conditions rapidly deteriorated Friday night, Todd wasn't sounding quite so bold.
"I'm not regretting staying," Todd said by phone. "But I'm not going to lie: There's a little bit of nervous tension right now."
LIVE BLOG: Hurricane Matthew
Todd said he was staying with friends at a third-story condo, which had lost electricity.
"It's throwing down right now," Todd said. "The trees are bending over. We saw a bush fly by. It's raining sideways now."
In Florida, the storm gouged out several large sections of the coastal A1A highway north of Daytona Beach and had nearly completely washed out the northbound lane for about a mile at Flagler Beach.
"It's pretty bad; it's jagged all over the place," said Oliver Shields, whose two-story house is within sight of the highway.
The deaths in Florida included an elderly St. Lucie County couple who died from carbon monoxide fumes while running a generator in their garage and two women who were killed in separate events when trees fell on a home and a camper.
About 500,000 people were under evacuation orders in the Jacksonville area, along with another half-million on the Georgia coast. More than 300,000 fled their homes in South Carolina. The latest forecast showed the storm could also scrape the North Carolina coast.
"We have been very fortunate that Matthew's strongest winds have remained a short distance offshore of the Florida and Georgia coasts thus far, but this should not be a reason to let down our guard," the Hurricane Center said in a forecast discussion.
St. Augustine, which is the nation's oldest permanently occupied European settlement and includes a 17th-century Spanish fortress and many historic homes turned into bed-and-breakfasts, was awash in rain and gray seawater that authorities said could top 8 feet.
"It's a really serious devastating situation," Mayor Nancy Shaver said of the city of 14,000. "The flooding is just going to get higher and higher and higher."
Historic downtown Charleston, usually bustling with tourists, was eerily quiet, with many stores and shops boarded up with plywood and protected by stacks of sandbags.
The city announced a midnight-to-6 a.m. curfew Saturday, about the time the coast was expected to take the brunt of the storm.
Matthew lashed Savannah, a city that was settled in 1733 and has a handsome historic district of moss-draped trees, brick and cobblestone streets, Greek Revival mansions and other 18th- and 19th-century homes.
Matthew was expected to bring winds of 50 to 60 mph that could snap branches from the burly live oaks and damage the historic homes. And 8 to 14 inches of rain could bring some street flooding. The extent of the damage wasn't clear early Saturday.
A small crew of workers Thursday set out to button up the Owens-Thomas house, one of Savannah's architectural gems. The 1819 Greek Revival mansion serves as a museum.
Sonja Wallen, a curator, said antique rugs and furniture were moved away from the home's more than 40 windows, many of them still with their original glass. Windows were fitted with plywood and other coverings, while sandbags were stacked at the basement entrance.
"It's basically a lot of little details - sandbags and duct tape around doorways where water can get in," Wallen said. "It's pretty much the same stuff you would do for any home."
At 5 a.m. EDT, Matthew had maximum sustained winds of 105 mph (165 kph), and was centered about 20 miles (130 km) southeast of Hilton Head, South Carolina. It was moving north about 12 mph (19 kph).
Airlines canceled at least 5,000 flights Wednesday through Saturday, including many in and out of Orlando, where all three of the resort city's world-famous theme parks - Walt Disney World, Universal Studios and SeaWorld - closed because of the storm.
But things began getting back to normal, with flights resuming in Miami and other South Florida airports. And power companies in Florida promised that electricity would be almost fully restored by the end of the weekend.
In areas the storm had already passed, residents and officials began to assess the damage.
Robert Tyler had feared the storm surge would flood his street two blocks from the Cape Canaveral beach. Tree branches fell, he could hear transformers exploding overnight, and the windows seemed as if they were about to blow in, despite the plywood over them.
But in the morning, there wasn't much water, his home didn't appear to be damaged on first inspection, and his vehicles were unharmed.
"Overnight, it was scary as heck," Tyler said. "That description of a freight train is pretty accurate."