New Orleans, Aug 31 (IANS): With people trapped on rooftops, flooded roads blocked by downed trees and power lines, and over one million residents without electricity, Hurricane Ida has wreaked widespread havoc since its landfall in the US state of Louisiana on the weekedn.

The hurricane was downgraded to a tropical storm over southwestern Mississippi on Monday, about 16 hours after making landfall in Louisiana as a Category 4 hurricane, the US National Hurricane Center (NHC) said.

However, it continues to leave a path of damage.

There are four flash flood emergencies in place for portions of southeastern Louisiana, according to a CNN report.

A tornado watch has been issued for portions of Mississippi, Alabama and Florida.

PowerOutage.US reported that the hurricane had triggered a massive blackout across the region, leaving at least 1 million customers in Louisiana and 80,000 more in Mississippi without electricity as of Monday.

Hundreds of boats, high-water vehicles and helicopters headed out on Monday across southern Louisiana in search of residents trapped on rooftops as floods overwhelmed their neighbourhoods.

In Slidell, Louisiana, Mayor Greg Cromer said there is water in "every neighbourhood in town" and local officials had to deploy boats to rescue 15 residents off their rooftops early Monday morning.

"In about a three hour period, we had probably five to six foot rise in the bayou and the lake estuary system that pushed water into a number of people's homes on the south side of our community," Cromer said.

At least one person was confirmed dead due to a fallen tree on his home in Prairieville, Louisiana, Ascension Parish Sheriff's Office said on Sunday night.

The 60-year-old man was pronounced dead at the scene.

Louisiana Governor John Bel Edwards told MSNBC on Monday that he "fully expects the death count will go up considerably throughout the day", as search and rescue efforts were underway.

Almost all of southeast Louisiana is without power and that all eight major transmission lines that feed electricity into the greater New Orleans area have failed, said the Governor.

Road and debris cleanup alone "is going to be a fairly long ordeal", he said.

Some New Orleans officials said it could be "weeks" before the power supply is restored, according to local media reports.

"The full extent of damage is yet to be seen," Louisiana state police said in a Facebook post, noting that search and rescue workers are still not able to access certain impacted areas.

President Joe Biden has declared a major disaster in Louisiana and ordered federal aid to supplement recovery efforts in the Ida-hit areas, the White House said.

"Assistance can include grants for temporary housing and home repairs, low-cost loans to cover uninsured property losses, and other programs to help individuals and business owners recover from the effects of the disaster," the White House said.

Ida landed on the 16th anniversary of Hurricane Katrina's strike, tying with 2020's Hurricane Laura and the Last Island Hurricane of 1856 as the strongest ever to hit Louisiana.