German police in the city of Frankfurt are bracing for left-wing demonstrations against government austerity measures and capitalism.

The Blockupy alliance says its activists aim to blockade on Wednesday the headquarters of the European Central Bank ahead of a ceremony inaugurating the bank's new building.

Blockupy says they are protesting government austerity policies that hurt ordinary people.

The ECB helps monitor compliance with the conditions of bailout loans for financially troubled countries such as Greece. Those include spending restraint and reducing deficits, policies blamed by some for high unemployment.

Frankfurt police say most demonstrators are expected to be peaceful, but that violence-prone elements could use the crowds as cover.

The ECB says it plans to be "fully operational" despite the police barricades, although some employees may work from home.