Hurricane Ida intensified over warm Gulf of Mexico waters and took aim at the U.S. Gulf Coast on Saturday, prompting tens of thousands in Louisiana and offshore energy workers to flee to safety.

Forecasters said it could make a U.S. landfall as an "extremely dangerous" Category 4 storm on the five-step Saffir-Simpson scale, generating winds of 140 miles per hour (225 kph), heavy downpours and a tidal surge that could plunge much of the Louisiana shoreline under several feet of water.

Ida's pace accelerated overnight and carried top winds of 85 mph (140 kph) as it headed northwest, the National Hurricane Center said on Saturday morning. The storm will continue to intensify rapidly over Gulf waters that are several degrees higher than normal, before coming ashore late Sunday.

Flooding from Ida's storm surge - high water driven by the hurricane's winds - could reach between 10 and 15 feet (3 and 4.5 metres) around the mouth of the Mississippi River, with lower levels extending east along the adjacent coastlines of Mississippi and Alabama, the NHC said.

Officials ordered widespread evacuations of low-lying and coastal areas, prompting an exodus that led to gasoline stations running dry and massive lines on highways leading from the shore.

Utilities were bringing in extra crews and equipment to prepare to restore electricity after the storm passes. Forecasters expect coming winds will cut power to hundreds of thousands of homes in the area.

Lifelong Gulf resident Hailey DeLaune, 29, told Reuters she and her fiance spent Friday evening boarding up the windows of his house in Gulfport, Mississippi, and gathering provisions to ride out the storm.

"Hurricanes have always been part of my life," said the high school theology teacher, who was born during 1992's Category 5 Hurricane Andrew. "You just run through your list and hope for the best."

Louisiana Governor John Bel Edwards, whose state is reeling from a public health crisis stemming from a fourth wave of the COVID-19 pandemic, urged residents to ready themselves for the hurricane immediately.

"Now is the time to finish your preparations," he told a Friday news conference. "By nightfall tomorrow night, you need to be where you intend to ride out the storm."

Edwards declared a state of emergency, and U.S. President Joe Biden issued a pre-landfall federal emergency declaration at Edwards' request. It authorized the U.S. Department of Homeland Security and the Federal Emergency Management Agency to coordinate disaster relief efforts in the state.

Edwards also said he had authorized activation of all 5,000 troops in the Louisiana National Guard for emergency deployments as needed.

U.S. energy companies reduced offshore petroleum production by nearly 60% and gasoline refiners were cutting operations at their Louisiana plants on the path of the storm. Some fuel prices rose in anticipation of production losses. 

CARIBBEAN TAKES FIRST HIT

On Friday, Ida smashed into Cuba's small Isle of Youth, off the southwestern end of the Caribbean island nation, toppling trees and tearing roofs from dwellings.

Jamaica was flooded by heavy rains, and there were landslides after the passage of the storm. Many roads were impassable, forcing some residents to abandon their homes.

Ida, the ninth named storm and fourth hurricane of the 2021 Atlantic hurricane season, may well exceed the strength of Hurricane Laura, the last Category 4 storm to strike Louisiana, by the time it makes landfall, forecasters said.

The region was devastated in August 2005 by Hurricane Katrina, which killed more than 1,800 people.