Bomb suspect in Brussels had cookies, salt

A man has been arrested in Brussels after telling police he had an explosives belt but only cookies and salt were discovered.

Belgian police have released six people without charges over an attack on a train last August. (AAP)

A man claiming to have been kidnapped and outfitted with a bomb belt has shut down a section of central Brussels during the morning rush hour but a bomb squad found only salt and cookies in the belt.

The man, identified only as JB, was taken in for questioning. Prosecutors said he had a criminal record and a history of psychiatric problems.

Brussels prosecutor Rym Kechiche said authorities were investigating whether the incident around the City 2 shopping mall had links to terrorism or whether it was a hoax.

A second man, who is suspected of driving JB to the scene, was also being questioned.

JB phoned police at 5.30am on Tuesday, saying he had been abducted and fitted with an explosive device that could be detonated remotely by another person, Kechiche said.

JB recently informed police that he had been enlisted to join the Islamic State extremist organisation in Syria, but Brussels prosecutors weren't able to prove or disapprove his claim, Kechiche said.

A car corresponding to a detailed description the man gave police was found parked in a street in the Schaerbeek area of Brussels.

Amid the alert, Prime Minister Charles Michel changed his morning program and a meeting of the Belgian crisis centre was called.

Crisis centre spokesman Peter Mertens said the nation's security alert was not changed.

"That level, and the measures accompanying it, is already high," Mertens said. "The situation of this morning has no impact on the existing measures."

At the scene, police in hoods and military wearing helmets were seen patrolling around at least one major entry to the City 2 shopping centre, and the demining squad was also called in. Some entries to the subway station were also blocked, and underground traffic disrupted.

Belgium has been living under a high threat level which says an attack is possible and likely since the November attacks in Paris. Some of the perpetrators of those attacks were either Belgian nationals or had lived in Brussels. Some have also been linked to the March 22 attacks on the Brussels subway and airport which killed 32.

The country has been particularly on edge over the last week following a series of arrests and police raids linked to suspected terror attacks.

Over the weekend, authorities charged three men with terror-related crimes after two days of raids and the detention of 40 people in a major investigation which they said required "immediate intervention".

Unconfirmed media reports suggested that a shopping complex, an American fast food chain and police were among the possible targets.