With effect Wed 27 Jan 2021 the Belgium Consultative Committee issued a ban on non-essential travel details of which can be found on https://www.info-coronavirus.be/en/news/occ-2201/. The information mentions that anyone travelling to or from Belgium will be required to carry a sworn statement, copies of which can be found here in English. This declaration for essential travel must be carried, from tomorrow, if you are crossing the Belgian border, please ensure you are following the most up to date travel information if you are planning a trip outside of Belgium.
https://www.info-coronavirus.be/en/travels/
https://diplomatie.belgium.be/en