Louisiana residents have boarded up buildings as they braced for torrential rain and strong winds from a strengthening Tropical Storm Barry.
The storm threatened millions as it churned a path to land and tested efforts to guard against flooding since Hurricane Katrina devastated New Orleans 14 years ago.
Officials predicted Barry would make landfall on Saturday morning near Morgan City as the first hurricane of the season, with the edges of the storm already lashing Louisiana with rain and leaving some coastal roads underwater.
As dawn approached on Saturday, more than 45,000 people in southern Louisiana had lost power.
The storm was expected to inflict the most damage on Louisiana and parts of Mississippi, with wind and rain affecting more than 3 million people.
Late Friday on night, residents received good news from forecasters. The Mississippi River is expected to crest in New Orleans at about 17.1ft on Monday, not 19ft as had been earlier predicted. The levees protecting the city range from about 20 to 25ft in height.
Governors declared emergencies in both states, and authorities took unprecedented precautions in closing floodgates and raising the barriers around New Orleans.
Governor John Bel Edwards said it was the first time all floodgates were sealed in the New Orleans-area Hurricane Risk Reduction System since Katrina.
Authorities told at least 10,000 people in exposed, low-lying areas along the Gulf Coast to leave, but no evacuations were ordered in New Orleans, where officials urged residents to “shelter in place”.
Before they did, people packed stores to stock up on bottled water, food and other essentials.
Forecasters said slow-moving Barry could unload 10 to 20in of rain through Sunday across a swathe of Louisiana that includes New Orleans and Baton Rouge, as well as south-western Mississippi, with pockets in Louisiana getting 25 in.
“It’s powerful. It’s strengthening. And water is going to be a big issue,” National Hurricane Center Director Ken Graham warned.
Rescue crews and about 3,000 National Guard troops were posted around Louisiana with boats, high-water vehicles and helicopters. President Donald Trump declared a federal emergency for Louisiana, authorising federal agencies to coordinate relief efforts.