Several metro stations in Brussels were closed on Wednesday after a shooting at the central Clemenceau station, the Belgian prosecutor's office said.
No injuries were reported, it said.
The suspects fled into the metro tunnels afterwards, a source close to the investigation said, adding that police were looking for two suspects.
Sources close to the investigation told local media the incident may have been drug-related.
Images on VRT's website showed two people walking into the station and opening fire. The images could not immediately be verified by Reuters.

24 dead after bus falls into river while boarding ferry in Bangladesh
Iran says it is reviewing US proposal to end war
UN Human Rights Council adopts resolution condemning Iranian attacks
273 million children out of school in 2026 UNESCO report
Russian attacks kill two in Ukraine's Kharkiv
Kuwait foils terror plot targeting state leaders
Iran rejects Trump's talk of negotiation as Israel and Iran launch airstrikes
Cyprus has opened discussion with UK over its bases, president says
