A 25-year-old man accused of ploughing a pickup truck into a crowd of spectators at a mardi gras parade in New Orleans has been arrested and charged with injuring 28 people, authorities said.

New Orleans police booked Neilson Rizzuto after taking him into custody in "a highly intoxicated state" immediately after the accident on Saturday evening (local time).

Rizzuto was charged with two counts of vehicular negligence injuring in the first degree, hit and run driving and the reckless operation of a motor vehicle, according to a statement.

No further information about Rizzuto was immediately available.

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The utility vehicle, travelling along the side of the street open to traffic along the Mid-City Krewe of Endymion parade route, struck three other vehicles, including a garbage truck, before veering onto the median strip where a crowd of people stood watching the procession, according to New Orleans police.

Mayor Mitch Landrieu in a statement referred to the suspect as a "drunk driver".

Twenty-one people were hospitalised after the crash, with five victims in serious condition.

Seven others declined to be hospitalised, city emergency services director Jeff Selder said.

The victims ranged in age from as young as three or four years old to adults in their 30s and 40s, Dr Selder said.

Among the injured was one New Orleans police officer.

Police Chief Michael Harrison said the officer, who was on duty, was undergoing tests to determine the extent of her injuries.

She was in "good spirits", he said.

Video footage shows pandemonium

Twenty-one people were hospitalised after the crash. ( AP: Chris Granger/NOLA.com The Times-Picayune )

Video footage from the scene showed pandemonium immediately following the early evening incident, but the parade, the largest and most popular of numerous mardi gras season parades in New Orleans, continued with little or no interruption.

The incident came during one of the busiest nights of mardi gras, when thousands of people throng the streets of Mid-City to watch the elaborate floats and clamour to catch beads and trinkets tossed from riders.

As police and city officials were assessing the scene, people were streaming home as plastic bags that used to hold trinkets and discarded beads littered the ground.

The area where the incident occurred was cordoned off with police barricades.

One woman at the scene told The New Orleans Advocate that a silver truck whisked by her, just feet away, as she was walking through the intersection.

The vehicle struck three others before ending up on the median strip. ( AP: Chris Granger/NOLA.com The Times-Picayune )

Carrie Kinsella said she "felt a rush it was so fast".

Twenty-year-old Kourtney McKinnis told the Advocate that the driver of the truck seemed almost unaware of what he had just done.

"He was just kind of out of it," she said.

The Federal Bureau of Investigation in New Orleans said its agents were "coordinating with our federal, state and local law enforcement partners to determine whether a federal violation has occurred".

The Endymion parade incident was not the only one to mar mardi gras festivities in New Orleans.

Earlier in the day, someone's gun went off accidentally in a portable toilet along the route of another, smaller parade, leaving one person wounded, police said.

Revellers leave the scene of the Endymion parade crash in New Orleans. ( AP: Gerald Herbert )

AP/Reuters