At least 21 people have died in catastrophic flooding in the state
Forecasters say Louisiana is "under the gun" of Storm Harvey after it made landfall for a second time.
At least 21 people have died after the storm caused catastrophic flooding in Houston and other parts of Texas, causing billions of dollars of damage.
The worst of the storm has passed to southern Louisiana, where flash flood warnings have been issued amid record rainfall and 45mph winds.
In Houston, there are fears that a weakened levee could fail and cause floodwaters in the Inverness Forest area to rise "very quickly and very fast."
Harris County official Jeff Lindner said that if the levee breaks, the water could reach the rooftops of homes in the immediate area.
Homes around the levee were subject to a mandatory evacuation order, but some residents chose to stay.
Texas governor Greg Abbott said "the worst is not over yet" for southeastern Texas, with flooding expected to persist for more than a week in some areas.
More than 24,000 National Guard personnel have been deployed and in recent days at least 8,500 people have been rescued, he added.
Officials fear that when floodwaters begin to recede in Texas, rescue workers will recover more bodies.
Among those confirmed dead was a Houston police sergeant who drowned as he attempted to drive to work.
In Beaumont, a woman was killed after she and her three-year-old daughter were swept into a rain-swollen drainage canal.
The child, who was rescued and survived, was found clinging to her dead mother.
Meanwhile, police say they have recovered the bodies of six family members whose van was swept off a bridge near Greens Bayou in Houston on Sunday.
Authorities are also investigating the deaths of 17 other people to see if they are storm-related.
More than 32,000 people are being housed in temporary shelters across Texas, while at least 50,000 homes are known to have suffered flood damage.
911 call centres have been besieged by more than 1,000 calls an hour from people seeking help in Houston.
Analysts are predicting the economic cost could reach $75bn (£38bn) in southeastern Texas alone.
On Tuesday, President Trump visited affected areas in Corpus Christi, Texas, telling rescue workers the flooding was of "epic proportion."
A day later, he tweeted: "After witnessing first-hand the horror & devastation caused by Hurricane Harvey, my heart goes out even more so to the great people of Texas!"
Harvey is forecast to move from Louisiana into northwestern Mississippi, Tennessee and Kentucky.
The National Weather Service is predicting 13 to 15cm of rain in western Tennessee.