New Orleans police say 21 people have been taken to hospital after a vehicle ploughed into a crowd watching the Krewe of Endymion parade in the Mid-City section of New Orleans.
12 of those are critically injured, local media are reporting the victims range in age - the youngest is said to be three years old.
Authorities say one person is in custody and they don't think it was an act of terrorism.
Local news outlet Times-Picayune reports the crash was reported Saturday at about 6:45 p.m local time.
New Orleans Police Department spokeswoman Ambria Washington says initial reports show so far that about a dozen people are in critical condition.
Ms Washington that number could increase as the investigation continues.