Law enforcers are reportedly treating the incident as a terror act.

Brussels is on its highest terror alert as the gunman, who appeared to have an assault rifle, remains at large, reported BBC.

Following the incident, French President Emmanuel Macron posted on  X: "I have just spoken with Prime Minister Alexander De Croo to express the solidarity of the French in this terrible moment that Brussels is going through."

"We think of the victims of this cowardly attack, as well as our Belgian and Swedish friends whose shock we share," he said.

A spokesman for the Belgian federal prosecutor, Eric van Duyse, urged people to go home and stay there as long as the threat has not been eradicated.

In a video posted on social media, a man identifying himself as the attacker said “he was inspired by the Islamic State” extremist group, Eric Van Duyse, said on the LN24 news channel as quoted by The Guardian.

Police have cordoned off the area after the incident.

Meanwhile, a video has gone viral on social media where a man, suspected to be the attacker, could be seen saying he carried out the attacks in the name of God.

An international football match being played between Belgium and Sweden in the city was abandoned following the incident.

Belgian Prime Minister Alexander de Croo confirmed on his X page that the victims were Swedish nationals.

"I have just offered my sincere condolences to @SwedishPM following tonight’s harrowing attack on Swedish citizens in Brussels," he said.

"Our thoughts are with the families and friends who lost their loved ones.As close partners the fight against terrorism is a joint one," he said.

Asking people of Brussels to remain vigilant, he said: "My deepest condolences to the relatives of this cowardly attack in Brussels. I am closely following the situation, together with the Ministers of Justice and Home Affairs from @CrisiscenterBE We are monitoring the situation and ask the people of Brussels to be vigilant."