Authorities in Waukesha, Wisconsin, said some people were killed and others injured when an SUV crashed into a Christmas parade.
The local police chief in Waukesha said the car had accidentally smashed into a crowded area, and more than 20 people were injured in the accident.
Initial reports indicated that 11 adults and 12 children were transferred to area hospitals following the accident.
A local CBS television reporter reported that at least one person was killed.
Some witnesses and local media reported that shots were fired from the car as it stormed the parade.
A video clip of the incident, which was posted on the Internet, showed a red SUV car breaking into the display, and it appeared that it was passing among more than 10 people.
In a second clip, the police appeared to open fire on the car as it hit a roadblock.
Local media reported that people near downtown Waukesha were asked to take shelter.
"We are closed due to an ongoing accident, please stay safe in your positions until further notice and take cover," Carroll University, which is close to the crash site, said in a tweet.