UPDATE: The M1 northbound has now reopened.
According to AA Roadwatch, Gardai are dealing with a collision on the M1 northbound at J16 Dundalk South in the hard shoulder and the left lane.
The M1 northbound is now closed.
There are reports that a car crossed the divide between the northbound and southbound lanes.
Traffic is slowing on approach and tailbacks are building.
More as we get it.