Hurricane Irma has weakened to a tropical storm, but is still proving deadly as it swirls beyond Florida flooding the coast and sending trees crashing onto homes.

The former hurricane remained an immense, 668km wide storm as its centre moved on from Florida on Monday afternoon, giving its still-formidable gusts and drenching rains a far reach.

Some 540,000 people were ordered to evacuate days earlier from Savannah and the rest of Georgia’s coast.

Irma sent more than a metre of ocean water into downtown Charleston, South Carolina, as the storm’s centre passed 400km away. In Atlanta, people nervously watched towering oak trees as the city, 400km inland, experienced its first tropical storm warning.

The body of a 62-year-old man who climbed a ladder behind his home was found under debris on the roof of his shed in southwest Georgia, where winds topped 65km/h.

Another man, in his 50s, was killed just outside Atlanta when a tree fell on his house, Sandy Springs police Sergeant Sam Worsham said.

And still another, Charles Saxon, 57, became South Carolina’s first recorded death when he was struck by a tree limb while clearing debris outside his home in Calhoun Falls amid wind gusts of about 65km/h, according to a statement from Abbeville County Coroner Ronnie Ashley.

Communities along Georgia’s coast were swamped by storm surge and rainfall arriving at high tide on Monday afternoon. On Tybee Island east of Savannah, Holland Zellers was grabbing a kayak to reach his mother in a home near the beach.

Downtown Atlanta hotels remained full of evacuees. Many milled about the CNN Center, escaping crowded hotel rooms in search of open restaurants. Many were glued to storm coverage on the atrium’s big screen. Parents pointed out familiar sites, now damaged, to their children.

About 800 flights had been cancelled at Hartsfield-Jackson Atlanta International Airport, which remained operational Monday, even as many planes turned corners of the tarmac into a parking lot.

For those contemplating driving around (down)town today…this seems to be a recurring theme. #JSO recommends not. pic.twitter.com/NSpvt1XV0q

— Jax Sheriff's Office (@JSOPIO) September 11, 2017

Downtown Atlanta’s streets were eerily quiet, with restaurants, businesses and schools closed. Traffic flowed easily on the city’s interstates, normally a sea of brake lights during rush hours.

More than 1.2 million Georgia Power and EMC customers mostly in coastal and south Georgia were without power. Alabama Power reported 45,000 outages. Utilities said thousands of employees were prepared to respond, but repairs could take several days.

Meanwhile shocked Florida residents are returning to their shattered homes as millions are left without power and roofs have been ripped off homes.

About 6.5 million people, about one-third of the state’s population, had been ordered to evacuate southern Florida to shelters, hotels or relatives in safer areas. 

Florida residents have begun the cleanup after Irma. Photo: EPA

High winds snapped power lines and left about 5.8 million Florida homes and businesses without power.

Authorities said the storm had killed at 39 people in the Caribbean with at least official one death in Florida, a man found dead in a pickup truck that had crashed into a tree in high winds on the Florida Keys over the weekend.

Irma, once ranked as one of the most powerful hurricanes recorded in the Atlantic, came ashore in Florida as a category four storm on Sunday and battered towns as it worked its way up the state.

The storm gradually lost strength, weakening to a tropical storm on Monday morning as it moved towards southern Georgia, the National Hurricane Center said.

It is expected to weaken to a tropical depression by Tuesday afternoon.

– With agencies