The leader of the far-right Alternative for Germany (AfD), the second largest party in parliament after Sunday's election, said Germany's likely next chancellor would be held hostage by left-wing parties that would seek to loosen tough fiscal rules.

Polls are open across Germany as the world’s third largest economy chooses a new leader to guide it through an era of febrile immigration debates and souring relations with Washington.

Germany's conservatives won the national election on Sunday, while the far-right Alternative for Germany came in second, its best ever result.