The Ring Road at Enfield in north Co Kildare (part of the Old N4 route) is closed following a collision.
Photos sent to KildareNow show that at least two vehicles were involved in the incident.
Debris can also be seen lying on the road.
AA Roadwatch said that traffic is very busy through the town as a result, with the queue back before the Newtown turn-off.
Gardaí have advised motorists to take the M4 as an alternative route.