Belgium's Euro 2024 qualifier against Sweden was abandoned at half-time for security reasons after two Swedish people were shot dead in Brussels.
Two men, both wearing Sweden shirts, were gunned down in the street before the game in Brussels.. The gunman fled the scene and is still at large.
Prosecutors say they are treating the shooting as terrorism.
Belgian police instructed Sweden fans to stay inside the King Baudouin Stadium for their own safety after the game was stopped.
UEFA said: "Following a suspected terrorist attack in Brussels this evening, it has been decided, after consultation with the two teams and the local police authorities, that the Uefa Euro 2024 qualifying match between Belgium and Sweden is abandoned. Further communication will be made in due course."
The Swedish players told UEFA that they did not want to play the second half and the Belgium team agreed, according to Swedish broadcaster TV6.
A statement from Belgium said: "Due to the incidents in Brussels earlier tonight, play is suspended. Our thoughts are with all those affected."
A Swedish FA social media post added: "Our thoughts go out to all the relatives of those affected in Brussels."
Sweden boss Janne Andersson told a press conference that shocked players decided not to carry on out of respect to the victims and their families.
"When I came down for the break, I got this information. Immediately, I felt that it was completely unreal. What kind of world do we live in today?" he told reporters.
"I came into the locker room and when the team started talking we agreed 100 percent that we didn't want to play on out of respect for the victims and their families."
Sweden captain Victor Lindelof told the press conference that the players never felt in any danger.
He said: "Our security team handled it well and put us at ease. They explained that this is the safest place to be in Brussels."
Fans were kept inside the King Baudouin Stadium until security services confirmed it was safe to depart, with the gunman at still at large.
As an extra safety measure, fans were allowed to enter the press room.
Footage from inside the stadium appeared to show fans clapping and chanting "Sweden".
The alleged shooter - who claims to be linked to ISIS - is still on the run hours after the horror unfolded at 7pm around three miles from Brussels' King Baudouin Stadium.
Cops in Belgium have now launched a terror probe following the shooting at Boulevard d'Ypres and the city has raised its terror alert to the highest level.
In a clip filmed moments before the horror, the alleged attacker says he's part of terrorist group the Islamic State.
Speaking in Arabic, he claims responsibility for the shooting and outlines what appears to be a terrorist manifesto.
The match was stopped as panic ensued among supporters - who were barricaded inside the stadium, which has capacity for 50,000 fans.
Thousands of terrified fans - including 700 Swedes - were trapped inside, with pictures showing fans phoning relatives and removing their jerseys as Belgium's Crisis Centre said it planned to "safely escort" them out.
Videos shared online shows the alleged gunman in a fluorescent orange jacket arriving on a moped just three miles from the Heizel stadium.
The alleged shooter then chases several people into a building while firing shots from an automatic rifle.
It is believed he first shot at a van, with one man dying inside.
Meanwhile, a third victim has been rushed to hospital.
No suspect has yet been arrested.
A second video shared on social media shows a man in an orange fluorescent jacket claiming responsibility for the attack.
Manhunt launched
Cops are now urgently hunting the gunman - and Belgium Prime Minister Alexander De Croo has asked residents to be "vigilant".
He said: "My deepest condolences to the relatives of the cowardly assassination attempt in Brussels
"I monitor developments together with the Ministers of Justice and Home Affairs from the national crisis center
"We are monitoring the situation and would like to ask the residents of Brussels to be vigilant."
Security services and ministers are currently gathered at a Crisis Center, amid fears of a terror motive.
The threat level for the Brussels Capital Region has been raised to level 4 - with officials telling locals to "avoid unnecessary movements".
Regions are placed under level four "when the threat is serious and very imminent".
Photos show a smaller gun left behind at the scene.
One witness told HBVL: "There was soon a crowd, including the police.
"I saw the victim less than five meters away from me. A man about 40 years old.
"And then a black Mercedes Vito with two or three bullet holes in it.
"Inside was the driver dead. The injured passenger, half his body filled with blood, but conscious."