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. Belgian police officers escort students from Brussels university ULB/VUB at the occasion of the Saint Verhaegen day, the founder of the Brussels university, after security was tightened in Belgium following the fatal attacks in Paris on Friday, in Brussels, Belgium, November 20, 2015 | Source: Reuters

"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 centre. Major shopping centres and stores did open on Saturday morning, with soldiers deployed outside shops.

However, many began closing their doors from around midday.

The crisis centre advised the public to avoid places with crowds, such as shopping centres, concerts, sports events or public transport hubs.

A sniper and an observer of Belgian police special forces are seen on a balcony of a building on Brussels Grand Place after security was tightened in Belgium following the fatal attacks in Paris on Friday, in Brussels, Belgium, November 20, 2015 | Source: Reuters

The city's museums and many cinemas and sports centres were shut, on separate orders from the city's 19 different local mayors. Clubs and venues cancelled 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 cancelled 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 cancelled 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.

Belgian soldiers patrol on Brussels Grand Place after security was tightened in Belgium following the fatal attacks in Paris on Friday, in Brussels, Belgium, November 20, 2015 | Source: Reuters