Belgian authorities have detained a suspect who was driving a car with gas canisters in his boot, setting off a security alert in the centre of Brussels.
The prosecutor's office said a busy part of the capital and a subway station was closed off during the evening rush-hour.
Prosecutor's spokeswoman Ine Van Wymersch said authorities did not want to take any chances and acted quickly "since the driver was known by judicial authorities and it was unclear why the gas canisters were there".
"We are taking the case seriously," Ms Van Wymersch added. She said the suspect was being interrogated.
Saint Gilles Mayor Charles Picque described the driver as "a radicalised person, so it was normal to take precautionary measures".
Ms Van Wymersch cautioned, however, not to jump to conclusions about a possible extremist motive.
The gas canisters were discovered when police noticed a car speeding and running red lights and pursued it.
The local transport authority said the Porte de Hal metro station closed on police orders while a perimeter was established above ground. Media reported an anti-bomb squad was brought in.
Belgian security services have been on high alert since suicide bombers attacked the Brussels airport and subway last March 22, killing 32 people.
Ms Van Wymersch said a bomb squad carried out two controlled explosions involving items from the car while the suspect was being interrogated.
No detonator or explosives were found, and only one of the two gas canisters was full, she added.