Anti-terror police detained three people for questioning following raids overnight in the Belgian capital Brussels, prosecutors said Friday.

The arrests took place as Belgium remains on high alert following deadly jihadist bombings in March and a machete attack against police officers a week ago.

"Three persons were arrested and taken for questioning," the federal prosecutor's office said in a statement, adding a judge would decide later Friday if there is enough evidence to keep them in custody.

The three identified as Wassime A., Asma A. and Malika B. were detained following eight raids Wednesday night that were ordered by a judge investigating terrorism cases.

It said no weapons or explosives were found in the six searches in the Brussels neighbourhood of Laeken, or in the one raid in Evere and the other in Anderlecht.

It was not clear whether the raids were linked to an investigation into another "possible threat" the prosecutor's office mentioned after it declared that bomb alerts on two Scandinavian airlines SAS planes from Oslo and Stockholm were false.

The two planes landed safely in Brussels on Wednesday and searches of the aircraft turned up nothing.

Belgium has been on high alert since suicide bombers struck Brussels airport and a metro station near the European Union headquarters on March 22, killing 32 people.

Those attacks were claimed by the Islamic State group, which controls large areas of territory in Iraq and Syria and has claimed numerous terror strikes in Europe over the last year.

A Belgian policewoman last Saturday shot and killed a machete-wielding Algerian man who wounded two female colleagues in the city of Charleroi, authorities said.

The Islamic State group claimed responsibility for the attack by the man who officials said had been living illegally in Belgium. (AFP)