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

The number of deaths in Haiti, the poorest country in the Americas, surged 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,” Obama told reporters after a briefing with emergency management officials about the fiercest cyclone to affect the United States since Superstorm Sandy four years ago.

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 US 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.

FOUR KILLED IN FLORIDA

Matthew sideswiped Florida's coast with winds of up to 120 mph (195 kph) but did not make landfall there. The U.S. National Hurricane Center (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.

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.

At 1:45 a.m. EDT (0545 GMT), Matthew's eye was about 95 miles (155 km) south-southeast of Charleston, South Carolina, and moving northward at 12 mph (19 kph), the NHC said. Wind gusts of more than 60 mph (100 kph) were reported in South Carolina.

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.

RELUCTANT TO LEAVE

Craig Fugate, director of the Federal Emergency Management Agency, said he was concerned that relatively light damage so far could give people up the coast a false sense of security.

“People should not be looking at the damages they're seeing and saying this storm is not that bad,” Fugate told NBC.

“The real danger still is storm surge, particularly in northern Florida and southern Georgia. These are very vulnerable areas. They've never seen this kind of damage potential since the late 1800s.”

In St. Augustine just south of Jacksonville, Florida, about half of the 14,000 residents refused to heed evacuation orders despite warnings of an 8-foot (2.4-meter) storm surge that could inundate entire neighborhoods, Mayor Nancy Shaver said in a telephone interview from the area's emergency operations center.

Television images later showed water swirling through streets in the historic downtown district of St. Augustine, the oldest U.S. city and a major tourist attraction.

“There's that whole inability to suspend disbelief that I think really affects people in a time like this,” Shaver said.