Almost 800 rescued in St. John the Baptist Parish after Hurricane Ida

The National Weather Service has issued a tornado warning for eastern Harrison County and northwestern Jackson County, both in southern Mississippi.

As Hurricane Ida approaches the Magnolia State, a severe thunderstorm capable of producing a tornado was located via radar over Biloxi in Mississippi's Harrison County early Monday at 2:46 a.m. CT. The "tornadic thunderstorm" was moving north at 65 miles per hour, according to an alert from the National Weather Service, which urged people to "take cover now!"

"Move to a basement or an interior room on the lowest floor of a sturdy building. Avoid windows," the National Weather Service said. "If you are outdoors, in a mobile home, or in a vehicle, move to the closest substantial shelter and protect yourself from flying debris."

The storm could impact the Gulfport–Biloxi International Airport as well as several miles of Interstate 10 and 110 in Mississippi, according to the National Weather Service. The tornado warning will remain in effect until 3:45 a.m. CT.

"Flying debris will be dangerous to those caught without shelter," the National Weather Service warned. "Mobile homes will be damaged or destroyed. Damage to roofs, windows, and vehicles will occur. Tree damage is likely."

-ABC News' Max Golembo

The emergency communications center for New Orleans said it is "experiencing technical difficulties" with its 911 system, after the city lost power due to Hurricane Ida.

"If you find yourself in an emergency, please go to your nearest fire station or approach your nearest officer," the Orleans Parish Communication District announced via Twitter early Monday. "We will update you once this issue has been resolved."

Ida has weakened to a Category 1 hurricane with maximum sustained winds of 75 miles per hour, as it continues to thrash Louisiana.

As of 1 a.m. CT, Ida was moving north at 9 miles per hour with the eye of the storm located about 20 miles south-southwest of Greensburg, Louisiana, and 45 miles from McComb, Mississippi, according to an advisory from the National Weather Service.

Ida is expected to continue heading north inland over southeastern Louisiana early Monday morning and later move into southwestern Mississippi, with further weakening forecast throughout the day. Ida is expected to be downgraded to a tropical storm later Monday morning, Nevertheless, the National Weather Service warned of continued threats from dangerous storm surge, damaging winds and flash flooding in parts of southeastern Louisiana.

In LaPlace, Louisiana, where up to 13 inches of rain has fallen from Ida so far, there were reports of high-water rescues to save residents trapped on top of homes amid completely flooded roads. The National Weather Service has extended a flash flood emergency for the area.

The National Weather Service also declared a flash flood emergency for Lafitte and Jean Lafitte, Louisiana, on Sunday night due to heavy rain and storm surge reportedly causing a levee to fail. Citing local law enforcement, the National Weather Service said more than 200 people were in "imminent danger" and urged people to "seek higher ground now!"

Heavy rainfall from Ida will continue Monday in southeastern Louisiana and spread northeast into the Lower Mississippi Valley. Total accumulations of 10 to 18 inches, with isolated maximum amounts of 24 inches, is possible across southeastern Louisiana into far southern Mississippi through Monday, according to the National Weather Service.

Storm surge, hurricane and tropical storm warnings remain in effect from Louisiana to the Alabama-Florida border. A tornado watch is also in place from Louisiana to the Florida Panhandle until 6 a.m. CT.

Ida is forecast to turn to the northeast on Monday and track across the Middle Tennessee Valley and Upper Ohio Valley through Wednesday, dumping rain throughout the region, according to the National Weather Service.

-ABC News' Max Golembo and Samantha Wnek

Entergy, Louisiana's major electricity provider, is reporting more than 130,000 customers without power in East Baton Rouge Parish as Hurricane Ida pummels the area, according to Baton Rouge Mayor Sharon Weston Broome.

DEMCO, the largest electric cooperative in Louisiana, is also reporting over 7,000 outages in East Baton Rouge Parish, which is home to some 440,000 people. Meanwhile, at least 20 roads are closed throughout Louisiana's most populous parish due to fallen trees and six structures have been heavily damaged, Broome said in a video message posted on Twitter early Monday.

"There could be more trees down overnight and more damage to structures," the mayor warned. "We need everyone to remain vigilant, to stay in your home because we want you and your family to stay safe."

Broome has issued a curfew for East Baton Rouge Parish from Sunday at 8 p.m. ET to Monday at 7 a.m. CT. She urged residents to "stay in as long as possible" to allow first responders, local officials and utility company workers to assess the damage and restore power to the area.

"The truth of the matter is, restoring power could take some time," Broome admitted.