Public-sector employees are staging a strike across Belgium, disrupting train and bus services as well as schools, prisons and mail delivery.
Belgium's state railway said domestic services in the country's French-speaking south ground to a halt today.
Some 40% of the trains in the Dutch-speaking north were still running.
A demonstration is planned by labour unions in the capital, Brussels, later in the day.
The unions are protesting at austerity measures approved by the Belgian government, including an increase in the retirement age.
Eurostar said all its trains are still running between London and Brussels.
However, some international Thalys trains between Paris and Brussels have been cancelled.
There will also be no Thalys service to Germany or the Belgian city of Liege today.