One person is in custody following the crash in New Orleans
Of the 21 people taken to hospital following the crash, five victims are said to be seriously hurt.
The incident happened during the Krewe of Endymion parade in the state of Louisiana at about 6.45pm local time.
One person has been taken into custody following the crash on suspicion of driving while intoxicated.
Children as young as three years old are among those injured - as well as a New Orleans police officer.
Investigators have stressed they do not believe it was a terrorist incident.
"We send a strong message about not drinking and driving, and about making smart decisions," New Orleans police superintendent Michael Harrison said.
Kourtney McKinnis told the New Orleans Advocate that the driver seemed almost unaware of what he had done in the aftermath of the crash.
"He was just kind of out of it," the 20-year-old said.
The incident happened on one of the busiest nights of Mardi Gras, with thousands of people descending on the city to watch elaborate floats and catch beads and trinkets thrown by performers.
