A person arrested during police raids in the Brussels neighbourhood of Anderlecht may be Najim Laachraoui, an accomplice of Paris attack suspect Salah Abdeslam, the newspaper La Libre Belgique and the broadcaster RTL report.
An official confirmation was not immediately available.
Laachraoui had been sought by police in connection with their investigation into the Paris attacks. According to some media reports, he may also have been involved in this week's terrorist attacks in Brussels.
Belgian federal prosecutors have scheduled a press conference for 1 pm (1200 GMT).