Emergency services are dealing with a serious crash on the Naas Road.
The incident happened at around 6.30am.
Commuters are facing major traffic delays, with tailbacks being reported at Newlands Cross.
Road closures and diversions are in place.
Gardaí say: "Traffic travelling outbound on the N7 Naas Rd is being asked to take the M50 to Tallaght (J 11) or Lucan (J7) and not to take Red Cow exit.
"From Tallaght (N81) traffic can continue to Saggart and rejoin at Rathcoole. From Lucan (N4) traffic can exit at J4 and go through Newcastle and rejoin at Rathcoole."