"The strike will continue until the situation is clearer and the workers decide to put it to an end," said Manuel De Castro, from the socialist FGTB union, which urged VW to safeguard the future of the plant amid fears it could eventually be shut down.
Belgian unions have called for a national demonstration in Brussels on Dec. 2 to put pressure on Volkswagen's management, De Castro said.
"We will do everything to get guarantees to keep our jobs," he said.
Volkswagen announced on Tuesday it would stop building the best-selling Golf in Belgium and would reduce the 4,900 staff in Brussels to 1,500 employees. It plans to transfer Golf production to two plants in Germany.
"I am pregnant and just bought a car. The circumstances are difficult," said Vanessa Hinnebaut, 26, who has been working at the plant for three years.
Manufacturing jobs are scarce in Brussels, where unemployment is running at over 20 percent. Volkswagen's cuts would leave major auto production in Belgium only at Ford's plant in Genk, Volvo's in Ghent and Opel's in Antwerp.
The restructuring caused considerable emotion in Belgium, including special news bulletins on television and radio and provoked criticism from Belgian Prime Minister Guy Verhofstadt, who said the decision was based on German national interests.
The reaction to the layoffs echoed the outrage caused by French carmaker Renault in 1997 when it decided to close the Vilvoorde plant in the suburbs of Brussels, cutting about 3,100 jobs.
Union officials addressing the crowd of workers pledged to fight the decision.
"We will stay united," a worker yelled into a microphone, addressing the crowd. Production at the plant had stopped.
The workers were joined by students and employees from surrounding firms.
"We came here to give them our support. This is our future too," said university student Bruno Stas, 21. The European Commission said on Wednesday it may be able to help the Belgian government assist the workers.
EU Regional Aid Commissioner Danuta Huebner met Belgian federal and regional employment ministers to discuss possible EU aid for the laid-off workers.
"We need to help the affected people to prepare for the labor market," she said, adding that EU funds might be available to help local authorities deal with the restructuring.
Volkswagen wants to cut up to 20,000 jobs in its German VW brand operations and reduce West European output by 20 percent, because the plants are not running at full capacity despite a rise in its market share.