German left-wing demonstrators burned tyres and hurled fireworks and stones in clashes with police and AfD supporters as the right-wing party's annual conference in Stuttgart.

Some 400 demonstrators were detained, a police spokesman said.

The protestors temporarily blocked access roads to the annual party conference of the Alternative for Germany (AfD), by setting car tyres on fire and forming human chains, police spokesmanLambert Maute said.

The clashes reflect growing social tensions in Germany.

Over 1 million migrants arrived in the country last year, emboldened by Angela Merkel's so-called open-door policy.

The violence lasted around four hours, delaying the start of the AfD’s two-day congress.

Some of the 1,000-strong demonstrators managed to assault some AfD party members.

One placard from demonstrators read “Your hate campaign pisses us off”. Another said “FCK AFD”.

The focus of the AfD’s conference was expected to be their anti-immigration and Islam-critical policies, plus its criticism of European Central Bank monetary policy.