Belgian police have detained a man near a central Brussels shopping centre, prompting a meeting of the prime minister and the national crisis response centre after initial suspicions he was carrying explosives.
A security source later told Reuters no explosives had been found on the suspect.
The area around the City2 shopping centre, a major commercial hub in the middle of the Belgian capital, was sealed off, although the nearby metro station was still open early on Tuesday (local time).
A spokeswoman for the Brussels prosecutor said the man was arrested at 5.30am and the army bomb disposal team was brought in to verify whether he was armed with explosives.
Television footage showed a large police presence in neighbouring streets
Belgium's crisis centre, which co-ordinates security measures, said it was holding a meeting, with Prime Minister Charles Michel and Interior Minister Jan Jambon present, to discuss the incident.
Michel had been expected to appear on an early morning radio show before rushing off to the meeting.
On Monday Belgian police released without charges six people who had been held for questioning over an attack on a high-speed train as it travelled between Amsterdam and Paris in August 2015.
In that attack, a man with a machine gun wounded two people on the train before being overpowered by passengers.
The new detentions on Monday followed a series of police raids on homes over the weekend, after which three men were charged with plotting an attack.
"They were released as planned after some checks," a spokesman for the Belgian federal prosecutor said. "There were no charges, either."