The perpetrator reportedly shouted out “Allahu Akbar” (God is Great) before causing the explosion, a witness said.
Belgium’s national crisis said the perpetrator had been “neutralised” and the situation was under control.
The incident took place around 1900 GMT, causing the city’s Gare Centrale to be evacuated. The nearby Grand Place, a major tourist destination, was also evacuated.
“I went down the mezzanine level, someone was shouting. Then he cried ‘Allahu Akbar’, and he blew up a trolley,” Nicolas Van Herrewegen, a railway sorting agent, told reporters.