THE A350 in Blandford St Mary is closed both ways between the A354 and Littleton Drove following a serious collision.
It is thought the road could be closed for some time while police officers carry out forensic examinations.
A police spokesperson said a car and a motorcycle were involved in the collision, which happened at 1.45pm.
"The road will remain closed for a considerable time," she said.
She added that officers would like to thank members of the public for their patience.