Hurricane Matthew killed more than 800 people and left tens of thousands homeless in its rampage through Haiti before it lashed Florida today with howling winds and rolled northward up the US Atlantic coast.
The number of deaths in Haiti, the poorest country in the Americas, surged to at least 842 today as information trickled in from remote areas previously cut off by the storm, according to a tally of death tolls given by officials.
Matthew, potentially the first major hurricane to 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.
"I just want to emphasize to everybody that this is still a really dangerous hurricane, that the potential for storm surge, loss of life and severe property damage exists," Mr Obama said after a briefing with emergency management officials.
"People continue to need to follow the instructions of their local officials over the next 24, 48, 72 hours."
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Matthew smashed through Haiti's western peninsula on Tuesday with 233 km/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.
The crew of NOAA research plane successfully flew through the dense clouds of Hurricane Matthew and into the eye of the storm. pic.twitter.com/rzWvz8TLUx
— RTÉ News (@rtenews) October 7, 2016
At least three towns reported dozens of people killed in the hills and coast of Haiti's fertile western tip, including the farming village of Chantal where the mayor said 86 people died, mostly when trees crushed houses. He said 20 others were missing.
With phone networks down and roads flooded by sea and river water, aid has been slow to reach hard-hit areas in Haiti.
Matthew skirted Florida today with winds of up to 195 km/h, but did not make landfall.
The city of Jacksonville in the northeast of the state could face significant flooding, Florida Governor Rick Scott said. The storm had cut power to some 827,000 households in Florida, he said.
This evening, Matthew's eye was brushing the northeast Florida coast, the US National Hurricane Centre said.
Its winds had weakened slightly and it was moving on a path that would likely take it near or over the coast of northeast Florida and Georgia through tonight and near or over the coast of South Carolina tomorrow.
No significant damage or injuries were reported in cities and towns in south Florida where the storm brought down trees and power lines, CNN and local media reported.
In Cape Canaveral, Florida, home to the country's main space launch site, the storm downed power lines and trees and destroyed billboards.
South Carolina officials warned residents of potentially damaging flooding and storm surge once Matthew arrives there.
