Mr Obama made his speech at Xavier University, which was hit by Katrina President Barack Obama has paid tribute to the people of New Orleans, five years to the day after Hurricane Katrina destroyed large parts of the city.
His administration would stand by them and continue rebuilding “until the job is done”, Mr Obama said.
Katrina was a natural disaster but also a man-made one, he said, which saw a “shameful breakdown” of government.
More than 1,800 people died when Katrina hit the Gulf coast in 2005.
The storm displaced hundreds of thousands of people, some of whom have still not returned.
Ceremonies in New Orleans to mark the anniversary include the tolling of the bells at St Louis Cathedral.
Across New Orleans, those who lived through Hurricane Katrina are marking the anniversary in very different ways.
Some are attending symbolic funerals for Katrina, a chance to try to put the past behind them and move on. But for others, the memories are too raw and their losses too great.
The city has made big strides over the past five years. Three quarters of the pre-Katrina population have returned and many more new residents have made New Orleans their home.
But neighbourhoods like the Lower Ninth Ward remain desolate and for the most part empty; there are those here who still feel forgotten. The Big Easy is not quite back but it is on the road to recovery.
President Obama acknowledged that much has been accomplished but that there is still a long road to full recovery. Five years ago, some thought New Orleans was finished but it is hard to kill the spirit of one of America’s most remarkable places.
Mr Obama made his speech at Xavier University – which, like much of New Orleans, was flooded when the levees protecting the city were breached by flood tides.
He described the city a symbol of resilience and perseverance in the face of tragedy.
A march and “healing ceremony” have also been scheduled in a district of the city where many houses still stand vacant.
“I’m tired of the anniversaries,” 77-year-old Barbara Washington told AP, explaining that she had been living in the suburbs since Katrina struck.
“I miss my home every day. I feel lost. But I also know we are getting back. We’re survivors.”
During a symbolic burying of victims of Katrina in Chalmette, Louisiana, residents were invited to write “farewell Katrina” messages and place them in a coffin, which was then buried.
“You made us stronger and made us realise what was important in life. One day we will feel better,” read one note.
Gregory Aymond, Archbishop of New Orleans, led the ceremony, telling the congregation: “Where was God five years ago on this day? Here, weeping with us, and trying to console us in the midst of a natural tragedy.”
Sources: US National Hurricane Center and US National Oceanic and Atmospheric Administration
Hurricane Katrina slammed ashore near New Orleans with winds of up to 125mph (201 km/h) – making it a Category 3 storm on the Saffir-Simpson scale. It had only just weakened from Category 5 and brought ashore a massive storm surge.
Entire communities on the Gulf Coast were obliterated, and than a million people were displaced and scattered around the US.
Many were housed in Federal Emergency Management Agency caravans.
Hundreds of thousands of people fled New Orleans and with much of its housing stock destroyed, the city’s population a year after the storm was only half its pre-Katrina level of 1.3 million.
According to US census figures, by July 2009, its population had recovered to 90% of its pre-storm level.
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