Eyewitnesses said the blast erupted on a crowded escalator deep inside the Oktyabrskaya station, just a few hundred yards from President Alexander Lukashenko's official residence. A spokesperson for Belarus' emergency services confirmed that there were "many casualties," but added that it was too early to stipulate the cause of the explosion.
Belarus, an independent post-Soviet state of around 10 million people, is closely allied with next door Russia. But it has no internal unrest akin to Moscow's ongoing security campaign against insurgents in the mainly-Muslim north Caucasus, and has never experienced the kind of terrorism that has hit repeatedly in big Russian cities, including a twin suicide bombing in Moscow's crowded metro that killed almost 40 people just one year ago.
"There were so many people down there at this rush hour, and the station is where people change trains, so there were lots of people there," says Yaroslav Romanchuk, a Belarussian opposition leader who passed through Oktyabrskaya station just five minutes before the blast. "People are stunned. This is the first time such a thing has happened in Minsk. It is difficult to say who might be behind it; we can only try to guess. I am lost. But I fear there will be no calm and peace here in Minsk any more."
Eyewitnesses quoted by the Belarussian news agency Belta said the blast collapsed an escalator full of people, leaving a huge crater behind. Amateur video, apparently shot on a cellphone and shown on Russian TV, showed people fleeing through underground corridors with smoke billowing from the station, but no panic.
Belarus has been rocked with internal discord since December presidential elections brought Mr. Lukashenko back for an unprecedented fourth term, amid widespread allegations that the voting was rigged. Lukashenko crushed opposition protests, arrested over 600 people – including 7 of his electoral rivals, and shut down most of Belarus' independent media.
The crackdown, which critics say is ongoing, deeply soured Belarus' relations with both the European Union and Moscow and left Lukashenko – a man often described as "Europe's last dictator" – looking more isolated than ever.
Andrei Bastunets, deputy chair of Belarus' independent Association of Journalists, says he fears authorities may blame the blast on political opponents, and use that to move even more harshly against internal critics.
"It's really difficult to say who could have done this," he says. "But there is already some concern that this tragedy will be used to step up pressure on representatives of the opposition."