The city's schools, universities and subway system remain closed Monday as authorities scramble to locate individuals they fear could be planning Paris-style attacks on Brussels, the country's capital and home of the main seat of the European Parliament.
But rather than give in to fear, Belgians have responded on social media with a defiant sense of whimsy. And cat pictures -- lots and lots of cat pictures.
The stream of cat pics was sparked when the country's federal police made a request on Twitter for the public to maintain silence about the ongoing counter-terror operations on social media, for fear of alerting potential targets of the raids to police movements.
Twitter users flooded the hashtag #BrusselsLockdown with cat memes, in a powerful gesture that showed they wouldn't lose their sense of humor over the terror threat -- and effectively buried any legitimate intelligence on police movements that might have been shared.
Through the time-honored medium of cute cat pics, they counseled each other to be brave.
They also poked fun at their predicament.
And they took subtle digs at the potential attackers responsible for it.
They gave mock updates on the counter-terror operations, featuring "hovercats"...
... and other state-of-the-art crime-fighting tech.
"This, dear outsiders, is how we fight terrorism here," tweeted Brussels resident Gilles Bordelais. "We haz kittenz!"
The response to the crisis brought a wave of admiring tweets from elsewhere in the world...
... and gave comfort to others facing a heightened threat of terrorism elsewhere.
Paris-based Twitter user Wendy Carrara tweeted a picture of a kitten looking at his reflection in a puddle, with a tiger staring back.
"We're stronger than we think!" she wrote.
Belgian federal police also appreciated their efforts. On Monday, they tweeted a symbol of their gratitude: a big bowl of cat food "for the cats who helped us yesterday."