'Mass casualty incident' declared after car ploughs into US Christmas parade, reports of multiple shots fired

Five are dead and over 40 injured after a car drove through a holiday parade in Waukesha, Wisconsin in the US in what's being described as a "mass casualty incident".

The incident happened shortly before 5pm (local time), the Journal Sentinel reported. 

"As we were walking back in between the buildings... we saw an SUV cross over, just put the pedal to the metal and just zooming full speed along the parade route. And then we heard a loud bang, and just deafening cries and screams from people who are struck by the vehicle," witness Angelito Tenorio told the newspaper.

In one video posted on social media, a red SUV appears to speed toward marchers from behind.

"The SUV does not slow & appears to try to hit as many as possible," said Kristen Barbaresi, a reporter from local news station CBS 58.

In a second video police appeared to open fire on the same vehicle as it crashed through street barriers.

A man at the scene told local news station Fox 6 most of his family had been taken to hospital.

"One man told me he saw about 30 people laying in the intersection of Main & Barstow," Fox 6 reporter Sam Kraemer said on Twitter.

"A woman who lives on Main St says she saw the SUV barrel through a dance team of girls between 9 and 15 years old.

"She says the immediate reaction was silence, followed by screaming, running, checking on those injured," Kraemer wrote.

The City of Waukesha confirmed several hours later that five people are dead and over 40 injured.

According to local police, the SUV has now been found parked in a driveway. Images of the vehicle show the bonnet severely crumpled and the fender hanging loose.

A "person of interest" has been identified and taken into custody.