BERLIN -- One fan died and another was taken to hospital after both suffered heart attacks during Borussia Dortmund's 2-0 victory over Mainz in the Bundesliga on Sunday.
One of the supporters died despite efforts to save him, while the other was "in a stable condition" in hospital, Dortmund media director Sascha Fligge said.
With the news filtering through during the match, fans broke into a rendition of "You'll Never Walk Alone" before the game ended, and then again after the final whistle -- when the Dortmund players lined up arm-in-arm as a mark of respect.
- Borussia Dortmund (@BVB) March 13, 2016
Dortmund president Reinhard Rauball said his club's thoughts were with the family and friends of the deceased fan.
"In the name of Borussia Dortmund, I wish to express my heartfelt sympathy and condolences to the families of those affected," Rauball told Sky Sport Deutschland.
"Our thoughts are with them."
Supporters were unusually quiet midway through the second half. Banners were taken down and the vast majority -- including Mainz supporters -- stopped chanting or singing for the rest of the game.
"At first I was irritated because I didn't know what was going on. In hindsight you have to pay the fans a huge compliment," said goalscorer Marco Reus, who said he had been asked by the referee why fans had stopped supporting the team.
- Henrikh Mkhitaryan (@HenrikhMkh) March 13, 2016
Dortmund's Japanese midfielder Shinji Kagawa did not even celebrate the goal which earned Dortmund all three points, with football not on anybody's mind by that stage.
"We were informed pretty quickly in the stands of what had happened," Rauball said.
"From that moment on, the game fell right into the background. I could no longer concentrate on it.
"The fans' reaction was spontaneous. I've never experienced anything like it.
"I can only pay a huge compliment to all of the fans for the way in which they expressed their sorrow and respect in this way, in a unified manner.
"I take my hat off to the Mainz fans who, without exception, joined us in mourning and stopped supporting their team.
"The scarves held in the air when 'You'll Never Walk Alone' was sung has my utmost respect. It shows how deeply rooted honour and respect of each other exists and can be expressed in such a short period of time, and I can only take my hat off to that."
Most Bundesliga clubs immediately showed their solidarity with Dortmund and paid their tributes to the deceased in response to a Tweet by Dortmund which confirmed what had happened.
"Prayers & thoughts to the fan we sadly lost today at the stadium, as well as to our 2nd fan now at hospital," tweeted Henrikh Mkhitaryan.
Information from Press Association and The Associated Press was used in this report.