Police threw a ring of steel around EU headquarters today as tens of thousands in a sea of banners from across Europe took to the streets in a worker backlash against painful spending cuts.
Similar demonstrations were planned across the continent, from Poland to Portugal and Latvia to Cyprus.
Police barricaded banks and shops and blocked access to the European Union building, where labour leaders hoped to mass up to 100,000 people from 30 countries in the afternoon to say "no to austerity".
Police were unable to provide immediate turnout figures but trade union sources and observers estimated tens of thousands were on the streets.
A total 148 people were detained preventively in collaboration with the organisers, said police spokesman Christian de Coninck, who described the detainees as "troublemakers carrying objects that had no place in the march."
"We're here to say 'no' to the multiplying number of austerity plans, whether adopted by governments or by European institutions," said Bernard Thibault, head of the major CGT French trade union, as the march took off.
"Our message is to avoid adding an unprecedented social crisis to the financial crisis, with the workers paying the cost."
Stepping off buses from as far afield as Germany, Poland and Britain for a march snaking across Brussels, protestors said they had travelled to the heart of the EU to show the human cost of budget cuts.
"We must make ourselves heard," said 28-year-old Polish policewoman Jelenia Gora after a 20-hour road trip under the Solidarity banner.
"We are here to tell the EU it must slow down cuts," said German miner Markus Machmik, 45, part of a group of 100 from the Ibbenbueren coalmine, dressed in white from hard-hat to boots.
The protest, the biggest such march since 2001 when 80,000 people invaded the Belgian capital, was timed to coincide with an EU plan to fine governments running up deficits.
Detailed proposals of the economic sanctions were released Wednesday by the 27-nation bloc's executive arm, the European Commission, ahead of a meeting Thursday of the continent's finance ministers.
"We will demonstrate to voice our concern over the economic and social context, which will be compounded by austerity measures," said John Monks, British general secretary of the European Trade Union Confederation.
Millions of jobs fell off the European map in the global downturn and many more look set to be squeezed as governments axe public spending.
As Europe tries to clean up its post-recession books, a backlash has begun focused on feared vast numbers of public sector job cuts.
In Spain, where unemployment has more than doubled, with one out of five workers jobless, pickets clashed with police Wednesday as unions launched a 24-hour general strike against tough labour reforms and spending cuts, provoking rush-hour chaos and forcing airlines to cancel flights.
Portugal's leading labour confederation, the CGTP, which is close to the communists, called protests in Lisbon and Porto hoping for more than 10,000 participants.
Poland's main unions, Solidarity and OPZZ, expected "several thousand" at a protest outside government headquarters.
Similar marches were scheduled in Cyprus, Greece, Ireland, Italy, Latvia and Serbia, with labour leaders across the board clamouring for growth and protesting the injustice of workers paying for the errors of the financial sector.
"This is a crucial day for Europe," said Monks, "because our governments, virtually all of them, are about to embark on solid cuts in public expenditures.
"They're doing this at a time where the economy is very close to recession, and almost certainly you'll see the economy go back into recession as the effect of these cuts take place."
A group from the GWU led by General Secretary Tony Zarb took part in the protest. The group earlier met John Monks, General Secretary of the European Federation of Trade Unions.