Hurricane Matthew, carrying winds of 195km/h, has lashed central Florida, hugging the Atlantic coast as it moves north and threatens more destruction after killing more than 800 people and leaving tens of thousands homeless in Haiti.
Matthew, the first major hurricane that could hit the United States head on in more than a decade, triggered mass evacuations along the coast from Florida through Georgia and into South Carolina and North Carolina.
Southern Florida escaped the brunt of the storm overnight, but US President Barack Obama and other officials on Friday urged people farther north not to get complacent.
"I just want to emphasise to everybody that this is still a really dangerous hurricane, that the potential for storm surge, loss of life and severe property damage exists and people continue to need to follow the instructions of their local officials over the next 24, 48, 72 hours," Obama told reporters after a briefing with emergency management and other officials.
The Florida city of Jacksonville could face significant flooding, Florida Governor Rick Scott said. The storm had cut power to some 600,000 households in the state, he told a news conference.
In the Caribbean country of Haiti, where poor rural communities were ravaged by Matthew, the death toll surged to at least 842 people, as information trickled in from remote areas previously cut off by the storm, according to a Reuters tally of death tolls given by officials.
Matthew smashed through the tip of Haiti's western peninsula on Tuesday with 233km/h winds and torrential rain. Some 61,500 people were in shelters, officials said, after the storm pushed the sea into fragile coastal villages, some of which were only now being contacted.
On Friday morning Matthew's eye, or centre, was brushing the Florida coast near the central city of Daytona Beach.
No significant damage or injuries were reported in West Palm Beach and other cities and towns in south Florida where the storm brought down trees and power lines earlier in the night, CNN and local media reported.
NASA and the US Air Force, which operate the Cape Canaveral launch site, had taken steps to safeguard personnel and equipment. A team of 116 employees was bunkered down inside Kennedy Space Centre's Launch Control Center to ride out the hurricane.
Matthew lessened in intensity on Thursday night and into Friday morning, the National Hurricane Centre said, but was still a Category 3 storm on the five-step Saffir-Simpson scale of hurricane intensity. Category 5 is the strongest.
It could either plough inland or tear along the Atlantic coast through Friday night, the Miami-based centre said.
The NHC's hurricane warning extended up the Atlantic coast from southern Florida through Georgia and into South Carolina.
Governor Scott has called on some 1.5 million people in coastal areas of Florida to evacuate and he continued to urge people to move away from danger on Friday.
As of Friday morning, about 22,000 people were in Florida shelters and more had moved inland or to the state's west coast, Scott said. Georgia and South Carolina had also opened dozens of shelters for evacuees.