Belgian armed police mounted raids across the country this evening after the prime minister announced another day of lockdown in the capital over fear that a Paris-style attack may be imminent.
"Different operations are under way because of the terrorist threat," a police spokesman earlier said before requesting that "the media do not comment directly on the actions under way, mentioning the places for example".
Shortly before 11pm, the public broadcaster, announcing several arrests, said the operations had concluded.
One of the prime suspects for the Paris attacks, Salah Abdeslam, is not understood to be among the those arrested.
La Libre (Belgian press): 6 arrested in police operation in centre of Brussels, one person injured, Salah Abdeslam not among those arrested
— Tony Connelly (@tconnellyRTE) November 22, 2015
Belgian Prime Minister Charles Michel said that Brussels' alert status will remain at the highest level as he said "we fear an attack like in Paris".
"The threat is considered serious and imminent," Mr Michel said, a day after authorities raised the alert level from three to four in the city that also hosts EU and NATO headquarters.
The city's metro system will stay closed and all schools will be shut tomorrow, Mr Michel said after a meeting of the national security council to review the situation.
He said the possible targets are commercial centres, shops and public transport and added that the army and police presence will be strengthened.
The alert status for the rest of Belgium will remain at level three.
Brussels was locked down for a second day today with armed police and troops patrolling near-deserted streets amid fears jihadists planned a repeat of the Paris attacks which left 130 people dead on November 13.
Mr Michel made no direct mention of the manhunt under way for several suspects linked to the attack, including Salah Abdeslam who managed to slip past French security forces after the carnage in Paris.
Salah Abdeslam's brother Brahim died when be blew himself up outside a bar as others attacked restaurants, a rock concert and the national stadium.
"What we fear are similar attacks, with several individuals in several places," Mr Michel told reporters.
"We are very aware that this situation is very difficult for everyone... we want to thank everyone for their efforts and everyone must remain vigilant," he said.
"We are doing everything possible to return to normal life."
The prime minister said officials would review the situation again tomorrow, given the disruption expected in Brussels.
Belgium has been at the heart of investigations into the attacks on 13 November after links emerged to Brussels, and the district of Molenbeek in particular.
Two of the Paris suicide bombers, Brahim Abdeslam and Bilal Hadfi, had been living in Belgium.
Salah Abdeslam is believed to have returned to Brussels from Paris shortly after the attacks.
Asked whether Brussels' maximum threat level since yesterday related to Salah Abdeslam alone, Interior Minister Jan Jambon said "unfortunately not".
"It is a threat that goes beyond just that one person," he said. "We're looking at more things, that's why we've put in place such a concentration of resources."
Bernard Clerfayt, the mayor of the Brussels district of Schaerbeek, was quoted as saying there were "two terrorists" in the Brussels area ready to carry out violence.
Mohamed Abdeslam, the brother of Brahim and Salah, urged Salah in an interview on RTBF television to give himself up, adding that he believed Salah was still alive because he had had a last-minute change of heart while in Paris.
There has been an increased level of security at Irish government buildings in Brussels, according to the Minister of State for European Affairs.
Army tanks and armed soldiers at the end of my street again this morning. Strange atmosphere to put it mildly in #Brussels.
— Luke 'Ming' Flanagan (@lukeming) November 22, 2015
Speaking on RTÉ's The Week in Politics, Dara Murphy said people should be aware that "those managing Irish Government units in Brussels are taking every step possible to ensure Irish people are safe".
He said security had increased for all European countries with offices based there.
Belgium has urged the public to avoid crowds in the capital, and also closed museums, cinemas and shopping centres. Clubs and venues have cancelled events.
Brussels Chief Rabbi Albert Gigi told Israel's Army Radio that the city's synagogues were shut over the weekend for the first time since World War II.
