Belgian TV is reporting that one of the suspected terrorists who was on the run has been arrested in police raids.
Abdelsam Salah, a Frenchman wanted in connection with the Paris attack, was arrested.
He is accused of having rented a car used to carry gunmen to the Bataclan music venue in Paris.
The Telegraph’s Gregory Walton adds that military paramedics are massing in the side streets off Delaunoystraat ahead of a possible further house raid.
He adds that grey military armoured battering rams were used in Molenbeek raid. Officers are wearing gas masks on the scene, and a specialist SEDEE bomb disposal unit deployed.
Meanwhile, a total of 23 people have been arrested and dozens of weapons seized in a series of raids on suspected Islamist militants across France, officials say.
The crackdown follows multiple attacks on bars, restaurants a concert hall and a stadium in Paris on Friday, in which 129 people were killed, reports the BBC.
A police operation is also reportedly under way in Brussels, Belgium, with reports that one suspect was arrested.
French PM Manuel Valls said the attacks were organised from Syria.
Meanwhile two more Paris attackers were named, along with five already identified. One is confirmed to have entered Greece as a migrant earlier this year.
France is to hold a nationwide minute of silence at midday local time (11:00 GMT) for the victims.
