Bucharest club Colectiv caught fire on Friday night.
The fire triggered a catastrophic stampede towards the exit, according to the BBC. The Romanian government says at least 27 people have died, with 155 more being treated in hospital. Some reports say the cause of the fire may have been fireworks being let off inside the venue, while another witness noted a spark on stage that ignited decor that eventually resulted in "an explosion and heavy smoke."
Colectiv was hosting a free rock concert that night, and up to 400 people may have been inside. The BBC reports that it was a converted factory with "two small exit doors, only one of which was possible to open initially."
Colectiv frequently held dance music events, with recent bookings including Baby Ford, Nicolas Lutz and Matthew Dekay. Saturday's event was meant to feature Danish DJ Nima Gorji.
Romanian President Klaus Lohannis said he was "shocked and deeply saddened" by the news.
"It is a very sad moment for all of us, for our nation and for me personally," he said in a post to his Facebook page.
The fire appears to be the deadliest nightclub blaze since a 2013 fire at a nightclub in Santa Maria, Brazil, killed 235 people.