A security alert in central Brussels sparked when a man was spotted wearing a coat with wires hanging from it has been declared a false alarm.

The man was isolated and kept under armed guard near a library adjacent to Royal Monnaie Opera while police investigated.

But authorities now believe the man was a student measuring radiation levels in the Belgian capital.

Police spokeswoman Ilse Van de Keere said no explosives were found and the man has been detained for questioning.

"Everything is under control," she added.

The incident came as Belgium remains on high alert after 32 people were killed in suicide blasts at Brussels Airport in March.

After the Bastille Day attack in Nice that left 84 people dead last week, security in Brussels has been further stepped up ahead of tomorrow's independence day celebrations.

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