Tropical Storm Michael took its drenching rains to Georgia and the Carolinas on Thursday after devastating Florida's Panhandle, killing at least two people, reducing homes to rubble and ripping up power lines and tree.
Michael crashed ashore on Wednesday near the small town of Mexico Beach as the third most powerful hurricane ever to strike the US mainland, carrying winds of up to 250 kilometres per hour and causing deep seawater flooding.
In large areas of Mexico Beach, homes were obliterated or reduced to stacks of rubble, aerial video from CNN showed on Thursday.
Brock Long, head of the Federal Emergency Management Agency, called the town "ground zero" for the hurricane damage.
One objective as recovery got underway was to help people who could be trapped in various areas along the coast, he told a news conference.
In Panama City, 32 km northwest of Mexico Beach, buildings were crushed and boats were scattered around.
Michael had left a trail of utility wires on roads, flattened tall pine trees and knocked a steeple from a church.
Al Hancock, 45, who works on a tour boat, survived in Panama City with his wife and dog.
"The roof fell in but we lived through it,” he said.
Florida Governor Rick Scott told the Weather Channel the damage from Panama City down to Mexico Beach was "way worse than anybody ever anticipated.”
It was not yet known what had happened to about 280 residents of Mexico Beach who authorities said had ignored evacuation orders as the storm approached the state's northwest.
The area is known for its small beach towns, wildlife reserves and the state capital, Tallahassee.
Michael was a Category 4 storm on the five-step Saffir-Simpson hurricane intensity scale, just shy of a rare Category 5, when it came ashore. It weakened steadily as it travelled inland over the Panhandle.
By 8 am EDT (5.30 pm IST) Thursday it had been downgraded to a tropical storm with 85-kph winds as it pushed through Georgia into the Carolinas, the National Hurricane Centre said.
Parts of North Carolina and Virginia could get as much as 23 cm of rain and life-threatening flash floods, the NHC said. The Carolinas are still recovering from Hurricane Florence last month.
The two people killed in the storm were a man who died when a tree toppled onto his house in Florida and a girl who died when debris fell into a home in Georgia, officials and local media said.
Long said several hospitals in the Panhandle were hit by the hurricane and patients had to be evacuated.
More than 830,000 homes and businesses were without power in Florida, Alabama and Georgia early on Thursday.
The hurricane, the fiercest to hit Florida in 80 years, pummeled communities across the Panhandle and turned streets into roof-high waterways.
"The wind that came through here was surreal. It destroyed everything," Jason Gunderson, a member of a group of rescue workers that calls itself the Cajun Navy, told CNN early on Thursday from Callaway, a suburb of Panama City.
"It's unlivable. It's heartbreaking."
Thousands of people hunkered down in shelters overnight after fleeing their homes ahead of the storm.
An estimated 6,000 people evacuated to emergency shelters, mostly in Florida, and that number was expected to swell to 20,000 across five states by week's end, said Brad Kieserman of the American Red Cross.
Thirty-two kilometres south of Mexico Beach, floodwaters were more than 2.1 metres deep near Apalachicola, a town of about 2,300 residents, hurricane centre chief Ken Graham said. Wind damage was also evident.
"There are so many downed power lines and trees that it's almost impossible to get through the city," Apalachicola Mayor Van Johnson said.
Michael had rapidly intensified as it churned north over the Gulf of Mexico in recent days, growing from a tropical storm into a Category 4 hurricane in about 40 hours and catching many by surprise.
With a low barometric pressure recorded at 919 millibars, the measure of a hurricane's force, it ranked as the third strongest storm on record to make landfall in the continental United States. Only Hurricane Camille on the Mississippi Gulf Coast in 1969 and the so-called Labor Day hurricane of 1935 in the Florida Keys were more intense.
US President Donald Trump declared a state of emergency for all of Florida, freeing federal assistance to supplement state and local disaster responses.
About 3,500 Florida National Guard troops were deployed, along with more than 1,000 search-and-rescue personnel, Governor Scott said.
Even before landfall, the hurricane disrupted energy operations in the Gulf, cutting crude oil production by more than 40% and natural gas output by nearly one-third as offshore platforms were evacuated before the storm hit.