Some 3,000 Opel workers and union leaders from across Europe protested on Wednesday against the threatened closure of the carmaker's plant in Belgium and plans to cut the workforce by a fifth.

More than 20 coachloads of workers arrived from Germany, filling the area with their yellow Wir sind Opel (We are Opel) T-shirts. A giant banner with the same logo hung from the Antwerp plant.

Union officials were also present from Britain, Spain, Poland, the Netherlands, Austria and Hungary.

The crowd held hands to form a giant circle in a field in front of the plant before union leaders took to the podium.

Europe without Opel-Saab-Vauxhall would be like a car without an engine, read one large banner.

Canadian automotive supplier Magna (MGa.TO) and Russian partner Sberbank (SBER03.MM) have agreed to buy a majority stake in Opel, the main European arm of General Motors GM.UL, and are in talks to work out the final details.

They plan to cut about 10,500 jobs from an Opel workforce of 50,000, half of whom work in Germany.

We're not prepared to accept plant closures anywhere in Europe, said John Fetherston, union representative for Ellesmere Port, one of two Vauxhall factories in Britain, the other being at Luton, north of London.

Peter Scherrer, general secretary of the European Metalworkers' Federation, told the crowd: We are here to show our solidarity with our Antwerp colleagues. If we do not fight it could be Bochum, Luton or Zaragoza tomorrow.

Magna has said it will keep all four German factories open and could close the Antwerp plant, which is losing production of the Astra hatchback.

UNIONS ACCEPT JOBS WILL GO

Local union chief Rudi Kennes, vice chairman of the European Employee Forum, said General Motors had promised Antwerp two new models in 2012, one for Opel and one for Chevrolet.

Worker representatives are due to meet Magna in Ruesselheim, Germany, on Friday. Scherrer told reporters the unions accepted the need for job cuts.

One is already too much, but we have to face reality, he said.

The European Commission issued a statement on Wednesday reiterating that it would examine whether Germany had tied 4.5 billion euros ($6.7 billion) in promised state aid to the preservation of plants there.

Any plant closure should be based solely on commercial considerations, although there is no consensus on these.

Opel's chairman Carl-Peter Forster has rejected a report in German magazine Der Spiegel that said Antwerp was more profitable than its rival site in Bochum, Germany.

Kris Peeters, the premier of Belgium's Flanders region, told the Flemish parliament on Tuesday that Opel's plant in Antwerp was indeed cheaper if adjustments were made to take into account the level of production.

Opel labor leader Klaus Franz told Reuters he hoped negotiations on staffing levels and productivity could be wrapped up quickly, reiterating labor's offer to chop 265 million euros each year from structural costs.

We all see the need for restructuring and capacity adjustments, but every job has a face that goes along with it and we want to do this in a socially acceptable way -- no plant closures and no forced layoffs, he said.

Opel's labor appeals to each European country not to encumber the talks with nationalistic interests.

($1=.6754 euros)

(Additional reporting by Marine Hass in Antwerp, Christiaan Hetzner in Frankfurt; writing by Philip Blenkinsop; Editing by Rupert Winchester, Greg Mahlich)

Germany Poland United kingdom