The Caragh/Prosperous Road (R409) is closed north of Caragh close to Mondello following an incident overnight.
At least two vehicles were involved, according to locals.
AA Roadwatch has advised motorists to use alternative routes.
The scene of the incident is close to the junction (above) with the L2004 local road towards Clane.
Diversions are in place at Cock Bridge and Donore.
Kildare Gardaí said described the incident as a 'serious road traffic Collision'.
They said the road will remain closed until tomorrow afternoon to facilitate an investigation.