Reports say a car and a lorry were involved in the collision at around 1.30am.
Crash investigators from Northamptonshire Police are on the scene but the road is likely to remain closed throughout the morning rush hour.
Diversion routes are signposted using the A6 between Chowns Mill and the A14, but drivers are being warned to avoid the Chowns Mill area where the roundabout is said to be gridlocked.
No information has been released regarding any injuries. The road reopened at around 11am.