Four raids took place, but no arms or explosives were found, a spokeswoman for the Brussels prosecutor's office told Belga news agency.

"The searches were carried out as part of an investigation by Brussels prosecutors," Ine Van Wymersch said. "While nothing was found, three people were taken in for questioning."

The raids took place late evening, with armed police reportedly setting up a security perimeter during the operation after carrying out house searches related to an anti-terrorism investigation.

The area was closed off to traffic as special police forces with machine guns moved in, a Reuters journalist said.

Molenbeek was home to several of those who took part in the so-called Islamic State-claimed November 2015 attacks in Paris and the suicide bombings of Brussels airport and the metro in March 2016.

Belgian authorities have been on high alert since the Brussels attacks in March 22, which killed 32 people.

jbh/kl (Reuters, AFP, AP)