Belgium put the capital Brussels on maximum security alert on Saturday, shutting the metro and warning people to avoid crowds because of a "serious and imminent" threat of coordinated, multiple attacks by militants.
A week after Paris bombings and shootings carried out by Islamic State militants, of whom one suspect from Brussels is at large, Brussels was placed on the top level "four" in the government's threat scale after a meeting of police, justice and intelligence officials.
Soldiers were on guard in parts of Brussels, a city of 1.2 million people and home to institutions of the European Union and the headquarters of NATO.
"The result of relatively precise information pointed to the risk of an attack along the lines of what took take place in Paris," Prime Minister Charles Michel told a news conference on Saturday after a meeting of the national security council. The Paris attacks left 130 people dead.
"We are talking about the threat that several individuals with arms and explosives would launch an attack perhaps in several locations at the same time," Michel said, adding people should be alert but not panic.
He declined to elaborate, but said the government would review the situation on Sunday afternoon.
The metro system is to remain closed until then, in line with recommendation of the government's crisis center. Major shopping centers and stores did open on Saturday morning, with soldiers deployed outside shops.
However, many began closing their doors from around midday.
The crisis center advised the public to avoid places with crowds, such as shopping centers, concerts, sports events or public transport hubs.
Belgian soldiers patrol in the arrival hall at Midi railway station in Brussels, November 21, 2015, after security was tightened in Belgium following the fatal attacks in Paris.
The city's museums and many cinemas and sports centers were shut, on separate orders from the city's 19 different local mayors. Clubs and venues canceled events, including a planned concert of veteran French rock singer Johnny Hallyday.
The agency has called on local authorities to postpone soccer matches, although most games in the top two divisions were set to go ahead.
Brussels-based Anderlecht's visit to Lokeren was canceled because the fixture was identified as a risk match requiring federal police, who were no longer available even with an increased military presence.
Foreign Minister Didier Reynders said that 1,000 troops were now available for patrols, double the level of a week earlier.
Stranded tourists on the cold and damp streets appeared more bemused than fearful, including Dutchman Gerrit Valkeman on a weekend trip with his wife.
"We had planned to visit museums, but are a bit puzzled about what to do now," he said at Place Royale, a square surrounded by museums and galleries.
Tour guide Stephane Bruno was planning to take a group of Americans around the city, but they canceled on advice from the U.S. embassy.
"My wife said not to go out today. But we were invaded by Napoleon and Louis XIV and were occupied eight times. We won't be defeated this time by terrorists," he said.
On normally bustling central shopping street Rue Neuve, Sofia Kostarako, a Greek national living in Brussels, said she had come out to show her sister Ioanna around.
"We will have a walk anyway. You can't change everything about your life. If something bad is to happen to you - it will," she said.
Belgium at heart of Paris attack probe
Belgium has been at the heart of investigations into the Paris attacks - which included suicide bombers targeting a France-Germany soccer match - after the links to Brussels, and the poor district of Molenbeek in particular, emerged.
Belgian soldiers and a police officer control the documents of a woman in a shopping street in central Brussels, November 21, 2015, after security was tightened in Belgium following the fatal attacks in Paris.
Fugitive suspected militant Salah Abdeslam, 26, slipped back home to Brussels from Paris shortly after the attacks, in which his elder brother Brahim blew himself up at a cafe. Fears of the risks he still poses prompted the cancellation last week of an international friendly soccer match in Brussels against Spain.
A second man from Molenbeek, Bilal Hadfi, was also among the Paris suicide bombers.
Three people detained in Brussels are now facing terrorism charges. Federal prosecutors said on Saturday that weapons had been found at the home of a person charged on Friday.
Belgian Interior Minister Jan Jambon told reporters he wanted a register of everyone living in Molenbeek because it was not clear at present who was at each address, a process local officials had already started.
EU interior and justice ministers in Brussels on Friday pledged solidarity with France and agreed a series of new measures on surveillance, border checks and gun control.
French authorities have said the attacks were planned in Brussels by a local man, Abdelhamid Abaaoud, 28, who fought for Islamic State in Syria and was killed in a police siege of an apartment in the Paris suburb of St. Denis on Wednesday.
Abaaoud's fingerprints were found on one of three AK47 assault rifles in a car left in eastern Paris, a source close to the investigation said, though it was not clear if he took part in the attacks or had just handled the weapon at some point.
The last time any part of Belgium was put on maximum alert was in May 2014 when an Islamist gunman shot dead four people at the Jewish Museum in Brussels. At that time, Jewish schools, synagogues and other institutions were put on level four.
The capital as a whole was last at the level four for about a month at the end of 2007 and the start of 2008, when authorities intercepted a plot to free convicted Tunisian Nizar Trabelsi. Brussels' New Year fireworks display was canceled.
Trabelsi was sentenced in Belgium in 2003 to 10 years for attempting to blow up a Belgian military base that houses U.S. soldiers. He was extradited to the United States in 2013.
Turkish police arrested a Belgian man of Moroccan origin on suspicion of having scouted out the Paris target sites.
A ban on demonstrations in the Paris area was extended on Saturday until Nov. 30, while a night curfew was imposed in parts of Sens, a town southeast of Paris, after raids there.