(AFP) The European Central Bank officially inaugurates its new 1.3-billion euro headquarters in Frankfurt on Wednesday, under tight security with more than 10,000 anti-austerity demonstrators planning a protest rally.

The ECB already moved into the 185-metre steel and glass towers, situated on the Main river running through Germany's financial capital, late last year.

But the spectacular skyscraper costing the equivalent of $1.4 billion will be officially inaugurated in the presence of ECB president Mario Draghi at 11:00 am (1000 GMT) on Wednesday, with between 60 and 100 invited guests.

Given the raging Greek debt crisis, the central bank has decided to keep the celebrations relatively low-key with just 20 guests from outside the institution.

A security zone has been erected a few hundred metres away to prevent any of the anti-capitalist protesters from getting anywhere near.

Marching under the Blockupy banner, groups such as Attac, but also unions will join in the rally, alongside representatives from Greece's leftist Syriza party, and Miguel Urban of Spain's Podemos.

Organisers estimate that at least 10,000 protesters will take part, with a special train of 800 activists arriving from Berlin and 60 buses from 39 different cities across Europe.

While police expect most of the protesters to remain peaceful, water cannon and helicopters are standing by in case the situation turns violent.

"It is one of the biggest deployments ever in the city," a police spokeswoman stated, adding that there was a "high possibility" that violence could erupt.

At a rally in Frankfurt in March 2012, a policeman was seriously injured when protesters went on the rampage in the city centre, causing around one million euros worth of damage.

At a subsequent demonstration in May 2012, there were around 20,000 marchers, but the rally remained mostly peaceful as more than 5,000 police sealed off large parts of the city.

'European project in danger'

"We see the European project in mortal danger. Instead of austerity and social cuts, we're calling for more democracy and a fairer balance of power in Europe and within the ECB," a number of unions wrote in a joint statement on Tuesday.

The activists are hoping to block access to the new building from 6:00 am (0500 GMT).

Demonstrators will then gather in the centre of Frankfurt at 2:00 pm (1300 GMT) and march through the city at 5:00 pm (1600 GMT).

The organisers accused the police and city authorities of "scaremongering".

One of the movement's spokesmen, Frederic Wester, said police were drawing up an "absurd civil war scenario".

Another spokesman described the massive police deployment as "a scandal".

But Hannah Eberle for the Interventionistische Linke (Interventionist Left) vowed that demonstrators "will not allow the police to get in their way".

"We're fighting for a different, a democratic and social Europe," said Roland Suess of the anti-capitalist group Attac.

Until last year, the ECB, which took over monetary policy in the single currency area in 1998, has been housed in a skyscraper, known as the Eurotower, in downtown Frankfurt.

But work began on a new headquarters, designed by Vienna-based architects Coop Himmelb(l)au, in 2008.

Incorporating the historic Grossmarkthalle, a wholesale food market, in the east of the city, the building was completed late last year, and the ECB actually moved into the premises shortly after.

Against the backdrop of tense talks over a Greek debt deal, the ECB is a prime target of anti-austerity protesters.

Earlier this year, the ECB stopped accepting Greek bonds as security in return for funding, when Greece's new hard-left government under Alexis Tsipras was elected on his promise to scrap the reform-for-aid bailout programme.

Blockupy brings together anti-capitalist and anti-austerity protestors from across Europe.

They camped out in tents at the foot of the ECB's Eurotower headquarters in Frankfurt for months in 2013.

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