Humberside Police tweeted: "Emergency services are currently dealing with an incident on the A180 at the Birchin Way roundabout and closures are currently in place.
"Please avoid the area were possible."
Sergeant John Rickells said: “It was good that people stopped and helped.
"It shows the good side of people and it all helps. We are also asking people who have not already spoken to us to contact us with what they saw and especially if they have dashcam footage.”
“We are still looking for CCTV so we can establish the circumstances."
A witness told GrimbsyLive that he heard a child screaming following the incident.
He said: "She was screaming in pain. It looked horrifying.
"But she had someone holding her.
"Those cries were heartbreaking to hear."
Another added they saw the girl fell out of the side door of the vehicle, before people rushed to her aid.
And another witness claimed they saw the girl being cradled in the middle of the carriageway.
A man, who was filling up his car with fuel at the time, wrote on Facebook that he "heard a commotion".
He added he then "saw this little girl laid in the road".
The man said: "I couldn't do anything to help, I just stood there in shock.
"I've never experienced anything so upsetting in my life.
"Hope she is ok."
More to follow...