0354 GMT January 21, 2018
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.
Four people were killed in the Dominican Republic, which neighbors Haiti.
Hurricane Matthew packed gusts of 160 kilometers per hour (100 mph) as it tracked north-northwest along Florida's east coast, the National Hurricane Center (NHC) said in an advisory. The storm's eye was 40 kilometers (25 miles) east of Cape Canaveral, home to the nation’s chief space launch site.
US President Barack Obama on Friday urged residents in the path of Hurricane Matthew to heed emergency officials' warnings, adding that although there has already been "significant damage," storm surge and flooding are still a major concern.
Roads in Florida, Georgia and North and South Carolina were jammed, and gas stations and food stores ran out of supplies as the storm approached early on Thursday.
Obama on Thursday declared a state of emergency in Florida, South Carolina and Georgia, a move that authorized federal agencies to coordinate disaster relief efforts.
Homes without power
About 600,000 Florida homes were without power on Friday due to the hurricane and more outages were likely, Governor Rick Scott told a news conference, as the storm moved near the state's Atlantic coast on a northward track.
"We're going to have more outages," Scott said, adding that there was a potential for significant flooding from the hurricane in the Jacksonville area. "The worst part of this is still to come. ... We still have potential for a direct hit and we're seeing 100-mile-per-hour winds."
NASA and the US Air Force, which operate the Cape Canaveral launch site, took steps to safeguard personnel and equipment.
No significant damage or injuries were reported in West Palm Beach and other communities in south Florida where the storm downed trees and power lines earlier in the night, CNN and local media reported.
In West Palm Beach, street lights and houses went dark and Interstate 95 was empty as the storm rolled through the community of 100,000 people.
Hurricane Matthew was carrying extremely dangerous winds of 195 kph (120 mph) on Friday, but is expected to gradually weaken during the next 48 hours, the hurricane center said.
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.
Few storms with winds as powerful as Matthew's have struck Florida, and the NHC warned of "potentially disastrous impacts."
Most powerful in 118 years
The US National Weather Service said the storm could be the most powerful to strike northeast Florida in 118 years.
A dangerous storm surge was expected to reach up to 3.35 meters (11 feet) along the Florida coast, Ed Rappaport, deputy director of the Miami-based NHC, said on CNN.
"What we know is that most of the lives lost in hurricanes is due to storm surge," he said.
Damage and potential casualties in the Bahamas were still unclear as the storm passed near the capital, Nassau, on Thursday and then out over the western end of Grand Bahama Island.
It was too soon to predict where Matthew might do the most damage in the United States, but the NHC's hurricane warning extended up the Atlantic coast from southern Florida through Georgia and into South Carolina.
The last major hurricane, classified as a storm bearing sustained winds of more than 177 kph (110 mph), to make landfall on US shores was Hurricane Wilma in 2005.