New Orleans remembered the dead and celebrated its painstaking comeback from disaster on Saturday, a decade after Hurricane Katrina ripped through the "Big Easy" leaving devastation and chaos in its wake.

City leaders placed wreaths at a memorial to Katrina's scores of unknown victims, marking the hour that the Category 5 storm struck with catastrophic force, overwhelming the Louisiana port's system of levees.

More than 1,800 people were killed across the US Gulf Coast when Katrina made landfall on August 29, 2005. A million people were displaced and the financial toll topped $150 billion.

New Orleans was plunged into a nightmarish scene of death and looting after Katrina barreled her way through and government help was painfully slow to come, something which still rankles in the city.

Mayor Mitch Landrieu, at a solemn ceremony attended by about 400 people at Charity Hospital Cemetery in the Mid-City neighborhood, struck a defiant tone.

"New Orleans will be unbowed and unbroken. We're still standing after 10 years," he declared.

"We have risen and we will rise again, but we can only do it if we hold each other up and we don't leave anybody behind."

The memorial to the unclaimed Katrina victims holds the remains of bodies which were never identified or claimed.

"We know that even as New Orleans is rebuilding, there are those who are grieving the deaths of their mothers, their fathers, their sisters. I want those families to know that our thoughts are with them," Governor Bobby Jindal said.

The wreath ceremony gave way to parades, marches and partying, capping a week of remembrance that included a visit from President Barack Obama.

Barbeque smoke and music filled the stifling New Orleans air, as brass bands and revelers celebrated the recovery of a city synonymous with Dixieland jazz and the raucous Mardi Gras.

Gwen Truhill, a local from the Ninth Ward, said: "We've come a long way, but yet still so far to go.

"It's good to see everybody come together and remember what happened, to see that people are still in good spirits. It's still kind of bittersweet."

Neighborhoods and cultural centers held parties and parades before former president Bill Clinton spoke at an evening commemoration, with performances by a number of Grammy-winning musicians.

- 'Sea of misery and ruin' -

Some 80 percent of New Orleans was swallowed up by floods which rose as high as 20 feet (six meters) after the low-lying coastal city's poorly built levee system burst from the pressure of a massive storm surge.

The water came up so fast that some people drowned in their homes. Hundreds more were stranded on their rooftops.

The few dry spots in the city descended into anarchy as tens of thousands of increasingly desperate people with little food or clean water waited for help to finally reach them.

"All of us who are old enough to remember will never forget the images of our fellow Americans amid a sea of misery and ruin," former president George W. Bush said in a visit to a New Orleans school Friday.

Bush, who faced intense criticism for his handling of the crisis, said he was moved by the city's determination to "rebuild better than before."

Ten years on, colorful homes on stilts have replaced many of the rotten hulks left behind by the stagnant and effluent-tainted flood waters.

Music and the smell of gumbo -- a spicy stew -- once again waft through the bustling streets of the French Quarter.

The tourism industry is booming once again, with nine million visitors last year and the city has managed to attract a growing number new businesses.

Crime -- while still high -- is improving, with the murder rate hitting a 43-year low in 2014 and the population in city jails down by two-thirds.

- Changing city -

Some of the city's 385,000 residents say its Creole and Afro-Caribbean identity has been altered indelibly by the storm.

A large portion of the population never came back and New Orleans now has 100,000 fewer people than it did before Katrina, and many are newcomers.

The black population has also fallen, from 68 percent of residents in 2000 to 60 percent in 2013, latest census figures show.

But plenty of white New Orleans residents also found the emotional and financial cost of rebuilding to be too high, though their numbers are harder to measure.

"A lot of things have changed, but sometimes change is for the better," city resident Elisianne Coco said.

"It's not the same New Orleans that it was when I was growing up, but as long as they get the best of it, that's all that matters."