Hurricane Michael is ravaging the Florida Panhandle with life-threatening winds, catastrophic storm surges and flooding rain.

The storm made landfall northwest of Mexico Beach, Florida as Category-4 hurricane Wednesday afternoon.

Its rapid intensification as it churned over the Gulf of Mexico caught many by surprise.

Coming ashore with maximum sustained winds of 250km/h, it is one of the most intense hurricanes to ever hit the US mainland, and the most powerful one on record to menace the Panhandle, a roughly 322km stretch of fishing towns, military bases and holiday beaches.

Michael battered the coastline with sideways-blown rain and crashing waves, swamped streets, bent trees, stripped away leaves and limbs and sent building debris flying.

There is “one hurricane-related fatality”, said Olivia Smith, public information officer for the Gadsden County Board of County Commissioners, adding the incident was “debris-related. There was a tree involved”.

Smith said the situation was dangerous even for emergency personnel. “We’ve been very cautious with sending our first responders out right now.”

The storm’s intensity waned steadily as it pushed inland and curled northeasterly into Georgia after dark. It was downgraded to a Category 1 storm, with top sustained winds diminishing to 120kph, about nine hours after it made landfall. But it was still considered an extremely dangerous storm.

Hurricane #Michael has made landfall just northwest of Mexico Beach, Florida. The latest public advisory is available on the NHC website: https://t.co/fniXaEmxWe pic.twitter.com/s4X21XtdX1 — National Hurricane Center (@NHC_Atlantic) October 10, 2018

Explosions apparently caused by transformers could be heard. Michael’s menace was compounded by its relatively quick development, growing from a tropical storm to Category-4 hurricane in about 40 hours.

Rainfall could reach up to a 30cm, and the life-threatening storm surge could swell to four metres. The storm appeared to be so powerful it is expected to remain a hurricane as it moves over Georgia early Thursday.

“We are in new territory,” National Hurricane Center (NHC) Meteorologist Dennis Feltgen wrote on Facebook. “The historical record, going back to 1851, finds no Category-4 hurricane ever hitting the Florida Panhandle.”

Only a couple of hours after Michael came ashore, floodwaters were more than 2.3-metres deep near Apalachicola on Florida’s Panhandle, NHC Director Ken Graham said.

Too late to evacuate

More than 2.1 million residents of at least 20 Florida counties had been under mandatory or voluntary evacuation orders.

Earlier on Wednesday, Florida Governor Rick Scott said on Twitter that it was too late to evacuate the target zone and that people who had stayed should immediately seek refuge.

The storm surge and waves from Hurricane Michael batter the beach in the Florida Panhandle community of Shell Point Beach, Florida [Mark Wallheiser/Getty Images/AFP]

President Donald Trump declared a state of emergency for the entire state of Florida, freeing up federal assistance to supplement state and local disaster responses.

NHC’s Graham said Michael represented a “textbook case” of a hurricane system growing stronger as it drew near shore, in contrast to Hurricane Florence, which struck North Carolina last month after weakening in a slow, halting approach.

He said the storm would still have hurricane-force winds as it pushed through Florida into Georgia and tropical storm-force winds when it reaches North and South Carolina, which are still reeling from post-Florence flooding.

Damaged buildings and a flooded street are seen after hurricane Michael passed through the downtown Panama City, Florida [Joe Raedle/Getty Images/AFP]

The region should brace for “major infrastructure damage”, specifically to electricity distribution, wastewater treatment systems and transportation networks, Jeff Byard, associate administrator for FEMA, told reporters on a conference call.

About 43,000 homes and businesses customers were already without power around midday.

Some of the storm’s most significant early impact was to offshore energy production. US producers in the Gulf cut oil production by about 40 percent and natural gas output by 28 percent on Tuesday, the Bureau of Safety and Environmental Enforcement said.

Residents fear they’ll lose everything

Many state offices, schools and universities in the area have been closed since Tuesday.

Among those who fled their homes was Betty Early, 75, a retiree who joined about 300 fellow evacuees huddled on makeshift bed rolls of blankets and collapsed cardboard boxes at an elementary school serving as an American Red Cross shelter in Panama City, near the storm’s expected landfall.

She was unsure how well her old, wood-framed apartment block would hold up. “I’m blessed to have a place to come,” she told Reuters news agency.

“My greatest concern is not having electricity, and living on a fixed income, losing my food.”

In the town of St Marks, John Hargan and his family gathered up their pets and moved to a raised building constructed to withstand a Category-5 after water from the St Marks River began surrounding their home.

Hargan’s 11-year-old son, Jayden, carried one of the family’s dogs in a laundry basket in one arm and held a skateboard in the other as he waded through calf-high water.

Hargan, a bartender at a riverfront restaurant, feared he would lose his home and his job to the storm.

“We basically just walked away from everything and said goodbye to it,” he told the Associated Press, tears welling up. “I’m freakin’ scared I’m going to lose everything I own.”

People wait for breakfast as they and others seek safety in a shelter as Hurricane Michael approaches Panama City, Florida [Brendan Smialowski/AFP]

About 2,500 National Guard troops were deployed to assist with evacuations and storm preparations, and more than 4,000 others were on standby. Some 17,000 utility restoration workers were also on call.

Meanwhile, neighbouring states were also making preparations

Georgia Governor Nathan Deal declared a state of emergency on Tuesday for 92 counties in his state.