A US flag blows in the wind in Atlantic Beach, Florida, on October 7, 2016, as hurricane Matthew approaches the area. Hurricane Matthew unleashed torrential rains and up to 120 mile-an-hour winds as it hugged the Florida coast Friday, after a blast through the Caribbean that reportedly left at least 400 dead in Haiti. (AFP/Jewel SAMAD)

WASHINGTON, Oct. 7 (Xinhua) -- About 800,000 families and businesses across the southern U.S. state of Florida on Friday were cut off power as killer hurricane Matthew continued to move up coast, posing a storm surge to coastal cities in U.S. southeast states.

According to projection by NextEra Energy Inc's FPL power company in Florida, Hurricane Matthew could knock out power to as many as 2.5 million customers in Florida.

As of 11 a.m. EDT (1500 GMT), U.S. National Hurricane Center said the hurricane had downgraded from a Category 4 hurricane to a Category 3 with sustained winds up to 120 mph, adding that the hurricane was moving to northwest.

Hurricane Matthew left devastation in its wake, killing hundreds of people in Haiti, before it moved toward the Bahamas and the United States.

Speaking at a press conference on Friday morning, Florida Governor Rick Scott warned that the "worst effects are still likely to come," referring to the possibility that hurricane could turn toward Florida's densely populated coast and cause a storm surge to coastal cities.

Meanwhile, in Georgia and South Carolina, local authorities and residents were bracing themselves for the most powerful storm to hit the U.S. southeastern region in about a decade.

Some 500,000 residents in Georgia's coastal areas had so far fled for inland areas, according to local media reports.

Speaking at a press conference, South Carolina Governor Nikki Haley sternly called out residents reluctant to leave, referring to possibly deadly flooding.

"This is the last time you will hear my voice when I am asking you to evacuate. We need everybody to consider evacuating and take this very seriously."