Exit polls suggest German Chancellor Angela Merkel’s Christian Democrats have lost control of Germany’s most prosperous state for the first time since 1953.
Merkel has been criticised for her handling of the euro zone debt crisis and her wavering policy on nuclear energy.
But losing control of the state of Baden- Wuerttemberg will be a body blow to her leadership of the centre-right government.
The state is one of Germany’s richest, home to automotive giants Daimler and Porsche.
Merkel angered voters there last year with her push to rebuild Stuttgart’s main train station, sparking mass protests.
Turnout is said to have been very high, suggesting voters have been galvanised by current issues.