Trade unions brought Belgium to a standstill Monday as the biggest general strike in years grounded flights, cut international rail links and shut sea ports in protest at the new government's austerity plans.

In the climax to a month of industrial action against new Prime Minister Charles Michel's policies, striking workers stopped public transport while most schools, businesses and government offices shut down.

The tension boiled over in isolated incidents of violence as union members torched a car in the port city of Antwerp and clashed with riot police outside the Brussels offices of a hardline Flemish nationalist party that is part of the coalition.

Pickets also blocked traffic outside the Brussels headquarters of the European Union. The 28-nation bloc has seen years of protests against austerity aimed at cutting debts that threatened the euro currency.

The 24-hour Belgian strike came days after a day of protest in Italy against Prime Minister Matteo Renzi's ambitious reform plans, while there have been similar demonstrations in Spain and Greece in recent months.

"There has never been a strike this strong," Marie-Helene Ska, the head of the Christian CSC union, was quoted as saying by the Belga news agency.

Belgian trade unions launched their movement last month with a march of more than 100,000 people in Brussels, which ended in violent protests that left dozens of police officers injured.

PM won't budge

Unions went ahead with Monday's general strike after premier Michel's right-of-centre government refused to budge on plans to save 11 billion euros ($13.7 billion) over five years.

His coalition, which took office in October, intends to raise the retirement age from 65 to 67 from 2030, scrap plans for a usually automatic cost-of-living raise next year and introduce public sector cutbacks.

Its plan got a measure of support from Edward Gardner, the International Monetary Fund's mission chief for Belgium who said the government has made "a very good start" but could go further, according to Belga news agency.

French-speaking Michel -- who at 38 is Belgium's youngest prime minister since 1840 -- heads a coalition of three Flemish-speaking right-leaning parties and his own Francophone liberals.

The government formed five months after elections had hoped to calm a nation deeply divided between the richer Flanders and the poorer French-speaking Wallonia, but instead has led to weeks of industrial action.

The last national strike in Belgium was in 2012 against the government of socialist prime minister Elio di Rupo.

Belgian airspace was closed after air traffic controllers joined the strike, preventing flights from landing or taking off from airports in Brussels, Charleroi, Liege, Antwerp and Ostend for 24 hours from 2100 GMT Sunday.

Some 50,000 passengers have been affected as a total of 600 incoming and outgoing flights have been cancelled at Brussels international airport, spokeswoman Florence Muls said.

'A real disaster'

"It's a real disaster" for the airports and passengers, Jean-Jacques Cloquet, managing director of Charleroi said on the RTBF news website, adding there would be a knock-on effect during the busy holiday period.

Eurostar rail services from Brussels to the British capital London and trains to the French capital Paris, Amsterdam in the Netherlands and the German city of Cologne were halted until early Tuesday.

The strike also paralysed activity in the port of Antwerp with 28 ships waiting to enter and 23 ships waiting to leave, a spokeswoman told AFP, although there were fewer problems at the port of Zeebrugge.

Belgian rail SNCB said domestic inter-city train services were cancelled and trams, buses and metro services were all cancelled, leading many people to take the day off work and stay home.

Most post offices were able to stay open despite the strike which also affected schools, nurseries, prisons and hospitals, where consultations and non-urgent operations were cancelled.