New Orleans was put under a curfew on Tuesday night.
The move came nearly two days after Hurricane Ida hit the coast of the US state of Louisiana, exactly 16 years after Katrina claimed more than 1,800 lives.
Four deaths have been confirmed and rescuers have started searching for the isolated.
The receding waters begin to reveal the extent of the damage along the US Gulf of Mexico coast.
A man is also missing, after being apparently killed by an alligator.
Read alsoHurricane Ida: the images of "catastrophic damage" in Louisiana
The city's mayor, LaToya Cantrell, has issued an order imposing an overnight curfew while most of New Orleans is still without power.
Images of people taken from flooded cars and destroyed homes are circulating on social media, but damage in the city itself has remained limited.
A person was also killed by a fall from a tree in Prairieville.
A second died while trying to drive in flood waters 95 km southeast of New Orleans, authorities said.
The human toll should increase
According to outage tracking site PowerOutage.us, Ida has left more than one million properties in Louisiana without power. Electricity was still not restored in most of them Tuesday evening. Electricity supplier Entergy announced Tuesday morning that electricity could be restored as early as Wednesday. The first to benefit will likely be hospitals, many of which have to cope with an influx of Covid-19 patients, wastewater treatment plants and water treatment centers.
In the state of Mississippi, where torrential rains fell, a road collapse left two people dead and ten injured, three of them in critical condition, police said. The death toll is expected to rise further, Louisiana Deputy Governor Billy Nungesser warned Tuesday, especially in coastal areas directly affected by Ida. US President Joe Biden has declared a major disaster for Louisiana and Mississippi, giving states access to federal aid.
Ida, now a tropical depression, moves northeast, threatening the Tennessee and Ohio valleys. Scientists have warned of an increase in hurricane activity, especially the power of hurricanes more than their number, due to the warming of the ocean surface. This rise in temperatures is due to climate change; it represents a growing threat to coastal communities around the world.
