Louisiana's devastating flooding is worst US disaster since Hurricane Sandy
Most of Louisiana has received at least one foot of rain since Friday — with some places getting as much as 30 inches, according to the National Weather Service. Although
More from NBC News:
Historic Louisiana Floods: More Than 40,000 Homes Affected
What Louisiana Flood Victims Need to Do Right Now
'Pray for Us': La Death Toll Rises as Thousands Lose Homes
The scale of the devastation was only starting to come to light.
"The current flooding in Louisiana is the worst natural disaster to strike the United States since Superstorm Sandy [in Oct. 2012]" said Brad Kieserman, the Red Cross's vice president of disaster services, operations and logistics.
He said in a statement Tuesday that the relief operation would cost at least $30 million — warning that the price tag "may grow as we learn more about the scope and magnitude of the devastation."
Grammy award-winning musician Taylor Swift said she was donating $1 million to flood relief because of the warm welcome she was given when kicking off her world tour in the state last year.
"The fact that so many people in Louisiana have been forced out of their own homes this week is heartbreaking," the 26-year-old performer said in a statement. "I encourage those who can to help out and send your love and prayers their way during this devastating time."
The Red Cross said volunteers from all 50 states, plus the District of Columbia and Puerto Rico, were helping thousands of residents get to a safe place, as well providing them with food and water.
Twenty parishes were under a federal disaster zone and more than a dozen were subject to overnight. At least 10 people have been arrested for looting in East Baton Rouge parish, according to Sheriff Sid Gautreaux.
Gautreaux told a news conference Tuesday that there were "significant" power outages and some homes and businesses had experienced "total devastation."
Among the worst affected was Livingston Parish, where more than three quarters of all homes have already been "lost to floods," Lori Steele, a spokeswoman for the parish, told NBC News.
"We're devastated in Livingston," Livingston Sheriff Jason Dore told the news conference.
Floodwaters were slopping over the top of the the Laurel Ridge levee, which protects the parish in the Baton Rouge metropolitan area from the Amite River, according to the Ascension Parish Homeland Security Office.
A third of Ascension's 45,000 homes have been flooded — and waters there are expected to rise.
"The next 24 to 48 hours is going to be a significant indication of just how much risk the parish remains in," said Rick Webre, director of the Homeland Security Office.
Forecasters said the worst of the rain is likely over, but the southern part of the state is still expected to see some 2 inches more rain through Friday, the NWS said.