Florida Keys facing potential ‘humanitarian crisis’ in Irma aftermath

began the colossal task of cleaning up after Hurricane Irma on Monday, as the remnants of the most powerful storm in Atlantic history limped north towards the

border.

Related: Hurricane Irma: 10 dead in

as record flooding hits northern

– latest updates

Daylight exposed the extent of the damage in the hardest-hit areas of the Florida Keys and the south-west coast, both whipped by the worst of Irma’s 130mph winds during the storm’s double landfall.

Officials in

warned of a potential “humanitarian crisis” in the Keys with military crews on standby with body bags for possible fatalities among those who failed to heed a mandatory evacuation order.

One resident told the Miami Herald the storm “sounded like war”.

In

on the west coast, where Irma made its second

landfall on Sunday, and in

to the north, authorities were assessing the impact of Irma’s storm surge.

But the effects of the hurricane’s long reach stretched across

. More than 5.5 million people were without power, 2 million of them in communities around the cities of

,

and

. Reports of property damage and beach erosion were widespread and pictures emerge of yachts smashed to pieces in wrecked marinas.

More than 6 million people, evacuated from their homes as Irma bore down on the state on Saturday as a deadly category 5 monster, anxiously awaited news about when they could return.

Five deaths were attributed to the storm in

, adding to its toll of more than 25 during its rampage across the

. In

on Monday search and rescue teams from the Florida Fish and Wildlife Department were sent into flooded neighbourhoods to reach stranded residents.

Donald Trump, who monitored the storm over the weekend from the Camp David presidential retreat, pledged the full resources of the federal government to assist the relief and recovery effort, which some experts estimate couldreach $290bn, combined with the cost of Hurricane Harvey’s strike on

last month.

Rick Scott, the

governor, was taking an aerial tour of the Keys and south-west

on Monday. “We’re really concerned to save every life there,” Scott said before the flight.

“We’re drawing every resource we can, locally, the state, the federal government. We have so much damage now around the state. Power lines are down, we have roads that are impassable. Everybody’s got to be patient as we work through this.”

All 7,000 members of Florida’s national guard were on duty, he said.

Video from the Keys, the low-lying island chain to the south of the state, revealed destroyed mobile homes and fields of debris strewn across US1, the only highway that links the archipelago to the mainland. The road was submerged by a storm surge of up to 15ft. On Monday sheriff’s deputies were blocking off access points to the Keys to returning residents, as rescue teams moved in.

Martin Senterfitt, emergency management director for

, said the US air force and air national guard had planes on standby to tackle what he called “a looming humanitarian disaster”.

Residents who remained in the Keys as Irma made landfall at

, about 20 miles from

, said the devastation was massive.

“About 5 o’clock in the morning when it really started to blow, the trees started snapping and we saw roofs getting ripped off,” Yeorgo Kapriris, who lives on

, told the Miami Herald. “The water came up about 5ft, we lost our van, we lost everything.”

On

and in downtown

, which suffered significant flooding in the business district of Brickell Avenue, maintenance crews were cleaning debris from the roads as the waters receded.

The entire south-east region remained under a city-by-city curfew to allow recovery crews to work and to free up law enforcement resources. In

and

counties, authorities reported more than two dozen arrests for looting.

Fears that south-east

and its 6 million residents would receive a first full-on strike from a major storm since Hurricane Wilma wrecked the area in 2005 eased when Irma took a late veer to the west on Saturday after moving north from the Cuban coastline.

Related: Evacuees face a desperate plight at

shelters as Irma strikes

Signing a federal major disaster declaration for

on Saturday, Trump acknowledged: “We may have been a bit lucky that it went on the west. It may not have been quite as destructive.”

In

, wind gusts of almost 100mph were recorded, accorded to the

-based National Hurricane Centre (NHC), before reporting equipment was blown away.

Barbara Sharief, the county mayor, told residents: “When we were in line for a direct hit from this monster storm we were bracing ourselves for the worst. Now I urge you to let the county’s recovery team do its jobs to ensure our community is safe before you resume your normal activities.”

The NHC downgraded Irma to a tropical storm early on Monday but warned it could still cause damage and flooding as it moved north towards its ultimate dissipation inland within 72 hours.

“Irma continues to produce very heavy rain and inland flooding across much of the northern peninsula and eastern panhandle of

and southern

, which is quickly spreading to the rest of the southeast United States,” NHC senior hurricane specialist Jack Beven said.

“Wind hazards will continue to spread north through

into portions of

,

,

and North Carolina.”