A man with psychiatric problems who was carrying a fake suicide belt full of salt and biscuits was arrested on Tuesday after he triggered a major anti-terror operation at a Brussels shopping mall, prosecutors said.

Belgium remains on a high state of alert after Islamic State-claimed bomb attacks in March left 32 people dead at the airport and at a metro station near European Union headquarters buildings.

Prosecutors said they were still investigating whether the man - who had once claimed he had been urged to join the IS group in Syria - had any genuine links to terrorism or not.

The 26-year-old man, identified only as J.B., called police to say he had been abducted in a car and dropped at the City 2 mall in central Brussels with an explosives belt that was to have been detonated remotely.

"After an initial inspection it was confirmed that it contained salt and biscuits. Any threat of an explosion has been initially ruled out," prosecutor's spokesman Rym Kechiche said in a statement.

"J.B. is known to the authorities for various incidents, including some linked to psychiatric problems," he said.

Police later located the car identified by the suspect in the Schaerbeek district of the capital and planned to question its owner.

Massive operation

The apparent threat had triggered a massive security operation.

Only one exit remained open at the nearby Rogier metro station, where soldiers checked passengers bags and belongings. Police and soldiers sealed off the immediate area, a reporter at the scene said.

Prime Minister Charles Michel called an emergency meeting of his security cabinet when the shopping mall alert was ongoing, reflecting the tensions in the country.

"The situation is for now under control. We remain vigilant," Michel said.

The terror alert level in Brussels remained at level three out of four, Belga news agency reported.

The City 2 mall had been mentioned in Belgian media in recent days as a possible target for attacks.

The incident comes only days after Belgian authorities charged three men with "attempted terrorist murder" after raiding dozens of homes linked to a reported threat to fans watching during a Euro 2016 soccer game.