Belgium raised its terror alert level to the highest level in the capital Brussels on Saturday, warning of an "imminent threat" in a statement from the OCAM national crisis centre.

"Following our latest evaluation... the centre has raised its terror alert to level 4, signifying a very serious threat, for the Brussels region," said the statement, which comes a week after the Paris attacks left 130 dead.

"The analysis shows a serious and imminent threat requiring specific security measures as well as detailed recommendations to the population," OCAM, which is part of the Belgian Interior Ministry, said in the statement.