The A38 is closed in Plymouth after serious multi-vehicle crash due to icy conditions.
One person is reported to be seriously injured in the collision, which reports suggest involved up to seven cars at Manadon Roundabout in Plymouth.
Tamar Bridge is closed eastbound between Pemros Road and Manadon Roundabout.
The road was closed at about 6.30am, with a serious knock on effect and gridlock reported.
A police spokesman said: "A number of vehicles had spun off the main road and onto the grass verges. At least one person was seriously injured as a result.
"The road has been closed at the Devonport and St Budeaux on slips. The Exeter bound carriageway is open from the Tamar Bridge but traffic is being directed off at St Budeaux.
"Diversions have been set up but there will be inevitable delays for the rush hours traffic. Officers at the scene believe that the freezing road conditions may be a contributory factor and are warning motorists to slow down when using any of the roads in the area.
"Further collisions on the approach to the scene are also adding to the congestion and motorists are advised delays journeys or avoid the area if possible.
East Cornwall has also been hit by the ice and cold temperatures, with some roads closed or impassible and schools closed or opening late.