The air ambulance was called to the A47 in Necton after a two car crash.
It was shut between the Tuns Road junction and McDonalds roundabout from 1pm for around two hours.
A man in his late teens suffered a head injury and was taken to the Queen Elizabeth Hospital in King's Lynn for treatment.
Four other people believed to be in the other car were treated at the scene for minor injuries.
Fire crews from Swaffham, Dereham and Watton released one person from a car using hydraulic rescue equipment.
They also made the vehicle and surrounding area safe.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here