At least nine people arrested and security operations staged in Tolouse, Grenoble and Brussels, among other places.
Belgium raised its attack alert in the capital to the highest level on Saturday, warning the public to avoid crowds because of a “serious and imminent” threat.
The move was made in Brussels after a meeting of top ministers, police and security services.
Prime Minister Charles Michel said the alert was “based on quite precise information” about a planned attack.
Speaking at a news conference, Michel said the fear was that “several individuals with arms and explosives could launch an attack … perhaps even in several places”.
“We urge the public not to give in to panic, to stay calm. We have taken the measures that are necessary,” he said.
The government’s crisis centre warned Belgians to avoid shopping centres, concerts, and public transport.
The alert for the whole country was raised a week ago following the Paris attacks to level three of the highest four, implying a “possible or probable” threat. Previously, only certain sites, such as the US embassy, were at level three.
A statement on the crisis centre’s website called on local organisers to cancel major events and football matches over the weekend.
Metro services in Brussels were also cancelled over the weekend.
Al Jazeera’s Paul Brennan in Brussels said despite the metro suspension, bus and tram services continued to run as normal.
“You would expect it to be slightly quieter on the weekend, and it is, but I have to say people are being rather stoic around here, and they don’t seem to have a huge amount of fear.
“There’s great concern in the wake of the Paris attacks; there’s great concern it will happen elsewhere, especially because of the manhunt that’s currently ongoing for one of the alleged Paris attackers, Salah Abdesalam.”
“He [Abdesalam] is believed to be in the Brussels area … and I think we can put two and two together that because he could be in the area, the government has decided to raise the threat level,” Brennan said.
Raffaello Pantucci, director of international security studies at the Royal United Services Institute, told Al Jazeera that Belgian authorities likely based their decision on specific information.
“They’re likely dealing with intelligence on some sort of offshoot group, and there’s also a suspect [Abdelsalam] on the loose,” Pantucci said.
“In some ways security measures being taken are an overreaction. Clearly we’ve seen across Europe a number of security scares this week… You do have these kinds of security responses after terrorist atrocities.”
Belgium has been at the centre of investigations after it emerged two of the suicide bombers had been living in the country. Three people detained in Brussels are facing terrorism charges.
Abdelhamid Abaaoud, the Belgian-born architect of the atrocity, was killed in a police raid in Paris’ Saint-Denis area, the Paris prosecutor announced on Thursday.
Abaaoud, a 27-year-old national of Moroccan origin, allegedly orchestrated the attacks claimed by the Islamic State of Iraq and the Levant (ISIL).