The closure is due to a collision and vehicle fire.
The A46 closed southbound between the A6006 and A607 near Syston (north).
The A46 is closed northbound between the A6 (Wanlip) and A6006 (Wymeswold).
Leicestershire Police are in attendance.
A full investigation is taking place.
It is anticipated that this closure will be protracted.
Delays are likely on the approach to this closure, with additional journey times also expected on diversion routes.
Southbound traffic is diverted via the A6006 and A607 southbound.
Northbound traffic is being diverted via the A6, A6004 and A6006.
The northbound diversion route is in place so that a low bridge will be avoided.