Hurricane Matthew killed almost 900 people and displaced tens of thousands in Haiti before plowing northward on Saturday just off the southeast U.S. coast where it caused major flooding and widespread power outages.

The number of deaths in Haiti, the poorest country in the Americas, jumped to at least 877 on Friday 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 triggered mass evacuations along the U.S. Atlantic coast from Florida northward through Georgia and into South Carolina and North Carolina. President Barack Obama urged people not to be complacent and to heed safety instructions.

“The potential for storm surge, loss of life and severe property damage exists,” he told reporters after a briefing with emergency management officials about the fiercest cyclone to affect the United States since Superstorm Sandy four years ago.

At 5 a.m. EDT (0900 GMT), Matthew’s eye was about 20 miles (30 km) south-southeast of Hilton Head, South Carolina, and moving northward at 12 mph (19 kph) with the storm packing 105 mph (165 kph) winds, the U.S. National Hurricane Center said.

Wind gusts of 80 mph (130 kph) in Hilton Head were reported early on Saturday by the NHC.

Hurricane Matthew: How to Help Haiti Victims

Matthew smashed through Haiti’s western peninsula on Tuesday with 145 mph (233 kph) winds and torrential rain. Some 61,500 people were in shelters, officials said, after the storm hurled the sea into fragile coastal villages, some of which were only now being contacted.

While highlighting the misery of underdevelopment in Haiti, which is still recovering from a devastating 2010 earthquake, the storm looked certain to rekindle debate about global warming and the long-term threat posed by rising sea levels to low-lying cities and towns.

At least three towns in the hills and coast of Haiti’s fertile western tip reported dozens of people killed, including the farming village of Chantal where the mayor said 86 people died, mostly when trees crushed houses. He said 20 others were missing.

“A tree fell on the house and flattened it. The entire house fell on us. I couldn’t get out,” said 27-year-old driver Jean-Pierre Jean-Donald.

“People came to lift the rubble, and then we saw my wife who had died in the same spot,” said Jean-Donald, who had been married for only a year. His young daughter stood by his side, crying “Mommy.”

With cellphone networks down and roads flooded, aid has been slow to reach hard-hit areas in Haiti. Food was scarce and at least seven people died of cholera, likely because of flood water mixing with sewage.

The Mesa Verde, a U.S. Navy amphibious transport dock ship, was heading for Haiti to support relief efforts. The ship has heavy-lift helicopters, bulldozers, fresh-water delivery vehicles and two surgical operating rooms.

For more on Hurricane Matthew, watch:

Matthew sideswiped Florida’s coast with winds of up to 120 mph (195 kph) but did not make landfall there. The NHC downgraded the storm to a Category 2 on the five-step Saffir-Simpson scale of hurricane intensity as its sustained winds dropped to 110 mph. Category 5 is the strongest.

There were at least four storm-related deaths in Florida but no immediate reports of significant damage in cities and towns where Matthew swamped streets, toppled trees and knocked out power to more than 1 million households and businesses. About 300,000 households and businesses were without power in Georgia and South Carolina, according to utility companies.

Two people in Florida were killed by falling trees, according to state officials, and an elderly couple died of carbon monoxide poisoning from a generator while sheltering from the storm inside a garage.

Hurricane warnings early on Saturday extended up the Atlantic coast from northeast Florida through Georgia and South Carolina and into North Carolina.

Flash flood warnings were also in effect as 15 inches (40 cm) of rain was expected to accumulate in parts of the region along with storm surges and high tides, the National Weather Service said.

Hurricane Matthew: 5 Ways to Deal with Damage Afterward

Several major roadways were flooded in Charleston, South Carolina, where water topped a wall at The Battery and was inundating White Point Gardens, a large downtown park, local media reported early on Saturday.

Standing water closed both directions of the Interstate 95 highway in Georgia. Some 8 inches (20 cm) of rain had fallen in the Savannah, Georgia area where Matthew downed trees and caused flooding of streets, local emergency officials reported.

Earlier on Friday in Daytona Beach, Florida the street under the city’s famed “World’s Most Famous Beach” sign was clogged with debris washed up by the ocean. The waves had receded by early afternoon but there was damage throughout the city, including a facade ripped off the front of a seaside hotel.

Though gradually weakening, Matthew was forecast to remain a hurricane until it begins moving away from the U.S. Southeast on Sunday, according to the NHC.

Federal and local officials warned residents along the coast that storm surges could still pose a danger by inundating entire neighborhoods with floods even as Matthew moves out of the region.