Belgian police fired tear gas and sprayed water cannons at rock-throwing demonstrators protesting European Union plans to cut social spending and raise retirement ages.

Police say about 20,000 protesters filled the streets of Brussels, where EU leaders are holding a two-day summit called to deal with the region’s debt crisis.

The meeting has been thrown into disarray because of Portugal’s political crisis. Portuguese Prime Minister Jose Socrates resigned Wednesday after parliament rejected his plans for more spending cuts. EU leaders fear Portugal could become the third member country to need a bailout from the EU and the International Monetary Fund.

EU leaders urged Portugal Thursday not to back down from plans to slash spending. Mr. Socrates will stay on as a caretaker prime minister until elections are held. He has said he will do all he can to avoid having to ask for a bailout.

But the Fitch and Standard & Poor’s agencies have both cut Portugal’s credit rating two notches, and some EU officials say a Portuguese bailout may be inevitable.

The EU and IMF granted Ireland and Greece multi-billion-dollar bailout packages last year, and some European financial analysts say Spain also might need help.