The 20-year-old French national blew himself up outside the Stade de France stadium last week during the Paris attacks.
Investigators say Hadfi had been living in Belgium and had spent time in Syria.
The raids are taking place in districts including Molenbeek, Uccle, Jette - places that have been described as a haven for extremists.
The Belgian prosecutor's office said the raids were targeting places "linked to Bilal Hadfi", including places associated with friends, family and people directly linked to him.
"It's a case which has already existed in 2015, following Mr Hadfi's departure for Syria," a source in the prosecutor's office told AFP news agency.
Police have detained one person in a separate raid in a suburb northwest of Brussels, Laeken, in connection with the Paris attacks but not linked to Hadfi, the unnamed source said.
Meanwhile, French PM Manuel Valls has warned that France could face a chemical attack from terror groups.
He made the comments as MPs vote on whether to extend the country's state of emergency by three months in the wake of the Paris attacks.
"Terrorism hits France, not because of what it is doing in Iraq and Syria [...] but for what it is. We know that there could also be a risk of chemical or biological weapons."
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