The departure hall at Brussels Airport, in Zaventem, has partially reopened, 40 days after multiple suicide attacks hit the airport and a metro train, killing 32 people and wounding at least 270 others.

Two attackers detonated suitcase bombs in the departure hall at the airport on March 22 before a third bomber blew himself up on a metro train in the Belgian city.

Both attacks were claimed by the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group.

On Sunday, Belgian flags were displayed on each side of a stage put up for the ceremony, with the date of the attacks and written tributes to the victims.

"We are back to the familiar scene of our passengers in the departure hall," said Arnaud Feist, head of Brussels Airport.

The messages in several languages included "Love beats hate" and "Violence will never be the answer".

On the floor in front lay bouquets of flowers, candles, photos of the victims and messages addressed to them.

Travellers were asked to arrive three hours before their flights to allow time for extra police security checks at the entrance to the departure hall.

About 400 passengers for only three flights were able to check in on Sunday afternoon in the departure hall, still relatively quiet compared with its usual bustle before the attacks.

The flights chosen were from Belgian carriers Brussels Airlines and Jetairfly TUI Airlines Belgium, to Malaga, Palma de Mallorca and Lisbon.

The airport was completely closed for 12 days after the attacks and has progressively been restarting operations, though it is not expected to return to full capacity until June.

Belgian police have arrested six people in raids as part of their investigation into the attacks.

Three men were charged by Belgian prosecutors with terrorist offences, including a suspect who local media said appeared on security footage with two suicide bombers at Brussels airport shortly before they detonated their bombs.

Authorities identified the suspect as Faycal C, although Belgian media reported his full name as Faycal Cheffou.