Hurricane Matthew weakened to a Category 3 storm overnight on Friday, but the National Hurricane Center (NHC) insisted that it remained "extremely dangerous" as it moved closer to the east coast of Florida.
It came after President Barack Obama declared a state of emergency for Florida, Georgia and South Carolina on Thursday, and Florida Gov. Rick Scott, begged residents to flee from the predicted landfall.
Hurricane Matthew packed gusts of 100 miles per hour (160 kph) as it tracked north-northwest along Florida's east coast, the National Hurricane Center said in an advisory. The storm's eye was 25 miles (40 km) east of Cape Canaveral, home to the nation's chief space launch site.
The NHC added that the center of the hurricane was expected to move "near or over" the East Coast of the Florida peninsula overnight on Friday and reach the coasts of Georgia and South Carolina on Saturday. The maximum sustained winds are forecast to be 120 miles an hour.
Matthew's winds had dropped on Thursday night and into Friday morning, downgrading it to a Category 3 on the five-step Saffir-Simpson scale of hurricane intensity, where it could either plow inland or tear along the Atlantic coast through Friday night, the Miami-based center said.
Few storms with winds as powerful as Matthew's have struck Florida, and the NHC warned of "potentially disastrous impacts."
The U.S. National Weather Service said the storm could be the most powerful to strike northeast Florida in 118 years.
Around 1.5 million people have fled Atlantic coastal areas as the storm nears land.
About 300,000 Florida households were without power, local media reported. In West Palm Beach, once lit street lights and houses went dark and Interstate 95 was empty as the storm rolled through the community of 100,000 people.
North Carolina Gov. Pat McCrory declared a state of emergency in all 100 counties in the state.
The declaration allows the Department of Homeland Security and Federal Emergency Management Agency to aid state and local responses to Matthew, which could cause tens of billions of dollars of damage to coastal areas.
Obama committed to providing necessary federal resources to help states respond to the hurricane in separate phone calls with the governors of Georgia, South Carolina, North Carolina and Florida. The president also asked those in affected areas to follow the guidance of emergency response officials.
Scott emphasized in a Thursday news conference the need to flee the storm, telling residents and visitors that "this is not something you should take a chance with, time is running out" and that "there are no excuses" for staying in an evacuation zone.
"You need to leave now," he implored. "Evacuate, evacuate, evacuate."
Scott reiterated those pleas later Thursday, saying "no one should be taking a chance." He urged people to evacuate to a storm shelter.
"Your safety, not comfort, is the most important thing," Scott said.
The governor said his state was expecting up to 8 inches of rain and wind of about 125 mph. Some eastern coastal areas can expect storm surge of 5 to 9 feet above ground level — with large waves towering above that level. Scott said about 1.5 million people are under evacuation orders.
Evacuations were under way in Florida, Georgia and South Carolina after Matthew, which hammered Haiti and Cuba, began battering the Bahamas.
The number of people killed by Hurricane Matthew in Haiti rose to at least 478 people on Friday, as information trickled in from remote areas previously cut off by the storm, officials said.
With the numbers rising quickly, different government agencies and committees differed on the total death toll. A Reuters tally of deaths reported by civil protection officials at a local level confirmed 478 had died.
Haiti's central civil protection agency, which takes longer to collate numbers, said 271 people died because of the storm. Some 61,500 remain in shelters, the agency said.
Georgia Gov. Nathan Deal encouraged residents to take heed of the mandatory evacuation.
"Well, we are not going to go drag anybody out of their houses against their will, but the mandatory evacuation designation is significant," he said in a news conference, explaining it is the highest warning the state can give for voluntary evacuations.
"I want everyone to understand we are being cautious, but we don't want anyone to panic," Deal said.
Scott said he was activating an additional 1,000 members of the Florida National Guard to help with evacuations, bringing the total to 2,500 active members. He also tweeted that he is asking Obama for additional resources to deal with possible power outages and flooding in the aftermath of the storm.
Miami Beach Mayor Philip Levine told CNBC that while the area does not have an evacuation order yet, it has closed schools and beaches and is "fully prepared" for the storm.
"We're there making sure everybody understands this is very, very serious," Levine said.
He urged residents to stay inside as the weather worsened later Thursday.
Correction: This story has been updated to correct the name of the Federal Emergency Management Agency.
—NBC News and Reuters contributed to this report.