The terror threat level for the Brussels region was raised to "maximum" on Saturday, with Belgium's Coordinating Body for Threat Analysis (OCAM) warning of a "serious and imminent" risk of an attack.

The city's underground metro system will be closed until at least Sunday afternoon, and trams will be limited to routes above the surface. Schuman railway station is also closed.

OCAM is advising residents to stay away from busy areas such as concert venues, railway stations and shopping centres.

Belgian prime minister Charles Michel said the terror threat level was increased because authorities received information of the risk of an attack "similar to Paris".

Michel said the decision to impose the maximum level 4 security alert came after OCAM heard of "relatively precise" information relating to "a threat of attacks committed by several individuals with weapons, perhaps in several places at once".

He said the potential targets were "shopping centers, public transport and big events".

There will be a reinforced police and army presence on the streets. Brussels Airport is outside the Brussels region, where the terror threat level remains 3 out of 4.

All shopping centres in the Brussels region will be closed on Saturday afternoon, including City2 and the Galerie Toison d'Or.

The Sound/Check festival at the Ancienne Belgique is cancelled, as is Johnny Hallyday's concert at Heysel tonight. The Atomium, Kinepolis, Bozar, Cinquantenaire museum, Muntpunt and the European parliament visitor centre are among the venues that have been closed.

Belgian Pro League football fixtures are going ahead as planned. Lower-division matches in the Brussels region are cancelled.