A man wearing a heavy coat with wires hanging out prompted a security alert and partial lockdown in central Brussels, but it turned out to be a false alarm, police said.

Authorities believe that 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 was detained for questioning.

"Everything is under control," Van de Keere said.

Belgium has been living under the country's second-highest terror threat level since November after the Paris attacks that killed 130 people. An extremist cell linked to those attacks was based in Belgium.Brussels was then hit by twin extremist attacks on March 22 that killed 32 victims.

Wednesday's incident occurred near a library adjacent to the Royal Monnaie Opera and lasted for about four hours because the man wasn't being cooperative at first, police said. Officers kept the man under armed guard, and a bomb squad was also called in as a precaution.

Eva Drees, who works in a nearby bookshop, said that early in the afternoon "we got asked by the police to evacuate the building. It all went very smoothly."

Because of the Bastille Day attack in the French city of Nice that left 84 people dead last week, security inBrussels was already increased for Belgium's independence day celebrations on Thursday.

Photo Sebastian Been