The third and final day of a national strike in Belgium on Wednesday grounded most flights at Brussels Airport and disrupted public transport.

The strike, organised by the country's main unions, is the latest in a series of protests against the coalition government led by Prime Minister Bart De Wever. Demonstrators oppose the government's proposed pension and labour market reforms.

Brussels Airport cancelled all departing flights as well as 110 of its 203 planned incoming flights.

Belgium's other main airport Charleroi Airport said on its website that it also expected significant disruption due to staff shortages and would be unable to guarantee scheduled landings and takeoffs.

Local media reported that the final day of the strike was expected to be the most disruptive with schools, public transport, and the private sector affected as well.

A protest is planned in Brussels for Wednesday afternoon. A similar demonstration in October drew about 80,000 participants.

"The budget message from the De Wever government is harsh: work longer and harder for less security regarding pensions, health and purchasing power," socialist Union ABVV-FGTB said on its website.

Gert Truyens, chair of the ACLVB liberal union, told the Belgian public broadcaster VRT he regretted unions had not been consulted by the national government.

"Agreements are not made in the streets at the picket lines; that happens at the negotiating table, but you need to be given the chance," Truyens said.

Although the government reached an agreement on next year's budget on Monday after months of tense negotiations, it did not avert the strike.

The government plans a new tax on banks and tax increases on airplane tickets and natural gas. Together with cuts in spending, this should lower the government deficit by 9.2 billion euros ($10.6 billion) by 2029.

The budget deficit of the euro zone's sixth-largest economy is set to hit 4.5% of gross domestic product this year, with debt of 104.7% of GDP, according to the central bank - well above the maximum agreed under EU budget rules.