Police were called at 11.30am to a report of a collision involving multiple vehicles near Coates.
Closures have been put into place on the A419 junction with the A429 and the A433 from Coates to the Thames Head pub.
These are expected to remain in place for a number of hours with motorists asked to plan their route in advance and avoid the area.
Emergency services remain at the scene.
Updates to follow.
