An anti-terror operation was under way at a shopping centre in central Brussels on Tuesday, Belgian prosecutors told the Belga News agency, adding that one suspect had been arrested and no explosives were found.
Prime Minister Charles Michel was holding an emergency meeting with members of his security cabinet, Belgian media reported.
The incident began at about 6:30am (0430 GMT) Tuesday after a report of a man acting suspiciously near the City 2 shopping centre triggered a bomb alert, broadcaster RTL reported.
A bomb squad team was deployed at the shopping centre, one of the main retail hubs of the Belgian capital.
Only one single exit remained open at the nearby Rogier metro station, where soldiers checked passengers bags and belongings.
Pictures showed police sealing off the immediate area.
Belgium is still reeling from the Islamic State suicide bombings at Brussels airport and on the city's metro on March 22 which killed 32 people and wounded hundreds more.
And the incident comes only days after Belgian authorities charged three men with "attempted terrorist murder" after raiding dozens of homes linked to a reported threat to fans during a Euro 2016 football game.
Prosecutors charged the three men, named as Samir C., Moustapha B. et Jawad B., but released nine others after questioning.
The areas searched included neighbourhoods in Brussels where November's jihadist attacks in Paris and the Brussels suicide bombings had planned their assaults.
Authorities said at the time they were responding to a need for "an immediate intervention".
Per capita, Belgium has produced the highest number of so-called foreign fighters in the EU who have travelled to wage jihad in Syria and Iraq, an estimated 500.
After Saturday's swoop, Michel said the country would be taking "additional and updated security measures."
However, he pledged that public events planned for the coming days would go ahead, he said, including those linked to the Euro championships.
"We want to continue living normally," the premier said.
And despite the lockdown in the area, the terror alert level in Brussels remained at level three, Belga reported.
On Saturday, a source close to Belgian authorities confirmed to AFP that several leading political figures have recently had their security increased.
According to state broadcaster RTBF and daily Flemish newspaper Het Nieuwsblad, 30 people and their families have had their personal security stepped up since Friday, including the prime minister, interior minister and justice minister.
Euro 2016 host France is also on high alert for possible attacks during the championship.