Four raids took place in the Molenbeek district but no arms or explosives were found.
Four raids took place in the Molenbeek district but no arms or explosives were found, the Belga news agency said, citing a spokeswoman for the Brussels prosecutor's office.
The gritty Molenbeek area was home to several of those who took part in the deadly Islamic State-claimed November 2015 attacks in Paris and the suicide bombings of Brussels airport and the metro in March 2016.
The authorities stepped up security after the killings and there have been periodic police raids and arrests since then as the investigations have continued.
Press reports said the Molenbeek raids took place late evening, with armed police setting up a security perimeter during the operation.
Belgian-born French national Salah Abdeslam, the only known jihadist to have survived after the Paris massacres, hid in Molenbeek and was arrested there four months later, on March 18, 2016, four days before the attacks on the Belgian capital.
Some 20 people have been charged in Belgium in connection with the Paris attacks. Investigators say the Paris and Brussels attacks were carried out by the same cell.