BRUSSELS (AFP) - Belgian Prime Minister Charles Michel on Saturday said the decision to raise the terror threat level in the capital Brussels to the highest possible level was linked to an imminent threat of attacks.

Brussels shut its metro system, cancelled public events and urged residents to stay away from crowded areas, with a gunman still on the run after the Paris attacks which have sent jitters through Europe.

"This was due to a threat of an attack by individuals with explosives and weapons at several locations in the capital," Mr Michel told a news briefing in Brussels.

Belgium's national crisis centre also added the Brussels airport, which is outside the city limits, and the immigrant heavy suburb of Vilvoorde to the top terror level.

A concert by Belgian-born rocker Johnny Hallyday, a major star in France, was also cancelled.

Early on Saturday, authorities warned of an "imminent threat" as Belgium-based extremists have been increasingly linked to the devastating attacks in Paris that left 130 people dead.

The security alert came hours after a suspect arrested in Belgium was charged with terrorist offences in connection with the Paris attacks.

The suspect, who has not been identified, is the third to be charged in Belgium over the deadliest terror attacks in French history.