Six officers were injured in the demonstration of around 2,000 steel workers, who gathered outside regional government offices in Namur.
The demonstrators threw stones and other small items at police, who fired tear gas and a water cannon in return.
Police said two officers were sent to hospital and four others sustained minor injuries.
The protesters are calling for the regional government to intervene and halt plans to close a coke plant and six production lines in the country, resulting in 1,300 job losses.
The leading steel and mining company blamed collapsing demand for steel and overcapacity in the sector for the planned closures in the area, which has a 200-year old steel industry.
Bernard Dehut, the chief executive of ArcelorMittal Liege, said the economic conditions made it "increasingly apparent that further action is required" to stem the company's losses.
The company said it would continue to operate five steel production lines which employ 800 people
The protest followed earlier demonstrations against the planned closures in Brussels.
Meanwhile in neighbouring France, Renault employees demonstrated against the company's new labour deal on the access road to the firm's factory in Flins, near Paris.
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