UPDATE: Gardai say a vehicle that was on fire has been cleared from the M7 Limerick/Dublin Rd northbound before J21 Borris-in-Ossory.
Traffic remains heavy at 17:25pm on Friday evening on approach but it is expected to ease shortly.
Motorists are urged to take care on approach and expect delays when travelling.
It is not known if any injuries have occurred.
The incident was reported to have happened around 15:40 on Friday afternoon.
Diversions are in place: To avoid the delays, divert off at junction 22 Roscrea, head towards Roscrea itself and then take the Old Dublin Rd (R445) back towards the M7 to rejoin at junction 21.