Grove Road is closed both ways near Portland Prison while a crane is being operated between Shepherds Croft and Incline Road.
The diversion is not thought suitable for larger vehicles.
The road is due to re-open at 6pm.
More top news
A driver has been jailed for more than seven years following a fatal collision in Nailsea last February.
South Crofty, between Camborne and Redruth, last produced tin in 1998 but beneath the surface are essential natural elements.
A young man's fallen to his death in a student block in Plymouth in what is understood to be a tragic accident.