"We must make this announcement now so that we can secure a viable future for the entire Opel and Vauxhall operations," GM Europe President Nick Reilly said in a statement.
The Opel site, which will close "in the course of 2010," employs 2,600 workers, the statement said.
Opel and its British sister brand Vauxhall have launched a programme of deep restructuring to salvage the core of loss-making operations under the direction of US parent company General Motors. Reilly, who is head of both GM Europe and Opel/Vauxhall, has said that 8,300 jobs will have to be cut from a total of more than 50,000 across Europe.
"It's an absolute catastrophe for Belgian workers and manufacturing," Walter Cnop, of the Belgian CSC union's metalworkers' branch, told AFP.
Cnop blasted management "arrogance" and a decision he said was "based on political considerations in no way assessed on economic grounds."
GM had initially planned to sell Opel/Vauxhall to a Canadian company and a Russian bank, but changed its mind in November and decided to restructure the carmaker and cut its output capacity by 20 percent. Opel/Vauxhall needs €3.3 billion ($4.65 billion) to carry out the restructuring, and directors have sought 2.7 billion of that from European governments which host the company's factories.