With just two Torpoint ferries operating there are also said to be 45-minute waits to cross at both Torpoint and Devonport.
The Devon and Cornwall Police traffic watch reported: "Reports of A38 Southbound blocked, slow traffic due to police incident on Tamar Bridge. In the roadworks area.
"Callers reports an incident on the bridge, closing the south side. Delays in both directions not helped by lane restrictions in place for bridge works."
The incident on the bridge involved concerns for the welfare of a man who police have now left in the care of health professionals.
Although police say all available lanes on the bridge are now open again there will be delays of up to 30 minutes while the traffic clears.