Officials said life-threatening conditions would last throughout Thursday, with Zeta crossing the mid-Atlantic states as a tropical storm before moving offshore around Delaware and southern New Jersey.
Louisiana governor John Bel Edwards said the most severe destruction — what he described as “catastrophic damage” — appears to be on the barrier island of Grand Isle in Jefferson Parish, where Zeta punched three breaches in the levee on the island.
Mr Edwards says he ordered the Louisiana National Guard to fly in soldiers to assist with search and rescue efforts, including door-to-door checks on property.
The governor also urged people to be cautious during the recovery.
“Oddly enough, it isn’t the storms that typically produce the most injuries and the fatalities. It’s the clean-up efforts. It’s the use of generators. It’s the carbon monoxide poisoning. It’s the electrocution that comes from power lines. So, now is the time to be very, very cautious out there,” Mr Edwards said.
A 58-year-old man drowned after being trapped in rising seawater in Biloxi, Mississippi, after taking video of the raging storm.
Leslie Richardson and another man were forced to abandon a stranded car and he desperately clung to a tree before his strength “just gave out”, officials said.
A Louisiana coroner said a 55-year-old man was electrocuted by a downed power line in New Orleans while in Georgia, authorities said a man was killed when high winds caused a tree to fall on to a mobile home in Cherokee County.
Power outages were reported across Louisiana, Mississippi, Alabama and Georgia, according to the website PowerOutage.us.
The storm raged onshore on Wednesday afternoon in the small village of Cocodrie in Louisiana as a strong Category 2 and then moved swiftly across the New Orleans area and into neighbouring Mississippi, bringing with it both fierce winds and a storm surge.
There was heavy rain at times but since the storm was so fast-moving, rain related flooding was not as much of a concern.
Waveland Mayor Mike Smith told WLOX-TV that his Mississippi Gulf Coast city, which was part of the area most heavily damaged by 2005’s Hurricane Katrina has maybe taken the worst hit since then from Zeta.
“We’re going to see a whole lot of damage in the morning,” Mr Smith said. Among the many trees blown down was one that fell on Mr Smith’s own house. “It was my next-door neighbour’s and he wanted to give it to me, apparently,” Mr Smith said.
Much of New Orleans and the surrounding area was without power on Wednesday night. The storm packed a punch as it whipped through the city.
Signs outside bars and restaurants swayed back and forth in the wind and palm trees along Canal Street whipped furiously. Officials said a person was taken hospital with minor injuries after a structure collapsed.
Echoing a plea made by officials across the Gulf Coast in the dark hours after the storm passed, New Orleans Mayor LaToya Cantrell implored residents to stay at home and let city officials assess the damage.
“Although we have made it through, we have been damaged, we have been hit,” she said.
Along coastal Louisiana, there were reports of some trailers flipped over, a petrol station destroyed, and downed power lines and trees.
Zeta had top sustained winds of 110mph as a Category 2 hurricane at landfall and is the 27th named storm of a record-breaking Atlantic hurricane season — with over a month left to go.
It set a new record as the 11th named storm to make landfall in the continental US in a single season, well beyond the nine storms that hit in 1916.