The A1 at Catterick in North Yorkshire is closed in both directions after reports of an explosion.
North Yorkshire Police said it received word of the explosion at 3am but there were no reports of any injuries.
Both slip roads to Catterick have also been closed and diversions have been put in place.
Motorists have been advised to avoid the area. The force said Catterick village was “heavily congested”.
A spokeswoman for the Highways Agency said the closure affected a six-mile (10km) stretch of road.