Every passenger travelling to Belgium from a country in the Schengen area is obliged to fill in the electronic Passenger Locator Form, published on the websites of the Federal Public Service Foreign Affairs and the Immigration Service, and submit it to the carrier before boarding.
If it is not possible for the passenger to use the electronic Passenger Locator Form, he is obliged to complete and sign the paper Passenger Locator Form published on the websites of the Federal Public Service Foreign Affairs and the Immigration Service and deliver it to the carrier. The carrier is obliged to deliver this statement to Saniport without delay.
The carrier is obliged to check that all passengers have completed a Passenger Locator Form prior to boarding. In the absence of this form, the carrier is obliged to refuse boarding.
Link to the electronic Passenger Locator Form:
https://travel.info-coronavirus.be/
Link to the paper Passenger Locator Form: https://dofi.ibz.be/sites/dvzoe/FR/Documents/BELGIUM_PassengerLocatorForm.PDF
Travel to Belgium from outside the Schengen area: On arrival in Belgium, the form must be handed over to the designated authorities at the border. This form can also be completed and sent electronically via https://travel.info-coronavirus.be/ where it is available in Dutch, English, German and French.
This is a sanitary measure imposed by the Federal Public Service Health, Food Chain Safety and Environment. Further information can be found on the form itself.
Source: https://dofi.ibz.be/sites/dvzoe/EN/Pages/Travel-to-Belgium.aspx