Tens of thousands flooded the streets of Brussels on Tuesday to protest against government austerity plans, as part of a national strike that has grounded flights and disrupted public transport.

Grappling with a budget deficit so big that it violates EU rules, the coalition government led by Flemish nationalist Bart De Wever is looking to reform pensions and make other savings that have infuriated trade unions.

"I am here to defend my rights and those of my pupils. If things continue like this, what future will they have?", teacher Victoria Coya told AFP at the Brussels march.

"I want our budgets to stop being cut," said the 27-year-old.

The demonstration drew an estimated 80,000 people according to police, while one union put turnout at around 140,000.

Brussels airport -- the country

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