Twin blasts hit Zaventem airport while the Belgian public broadcaster RTBF reported a second blast striking a metro station in the capital shortly afterwards.
Terrified people running from the terminal as plumes of smoke rising to the sky were shown in the footage of the incident that emerged online following the back-to-back explosions.
The local media reported that up to 12 people had been killed, however the authorities have not confirmed the toll formally so far.
Zaventem airport in Brussels is the main international airport which was evacuated following the back-to-back explosions.
The deadly attacks on two key areas in Brussels follows four days after the security forces arrested a suspected participant in November militant attacks in Paris that killed 130 people.