SKOPJE, North Macedonia (AP) — A massive nightclub fire killed 51 people early Sunday in North Macedonia ’s eastern town of Kocani, and injured about 100 more, interior minister Panche Toshkovski told a press conference.

The blaze broke out around 2:35 a.m. during a concert by a local pop group, according to Toshkovski. He said the young clubgoers used pyrotechnics that caused the roof to catch fire. Videos showed chaos inside the night club, with young people running through the smoke as the musicians urged people to escape as quickly as possible.

This is the worst tragedy in recent memory to befall the landlocked nation, whose population is less than 2 million.

“This is a difficult and very sad day for Macedonia. The loss of so many young lives is irreparable, and the pain of the families, loved ones and friends is immeasurable,” Prime Minister Hristijan Mickoski wrote on X, formerly Twitter.

“The people and the government will do everything in their power to at least slightly alleviate their pain and help them in these most difficult moments.”

Officials said the injured have been taken to hospitals around the country, including the capital, Skopje, many with severe burns. The effort was being assisted by multiple volunteer organizations.

Family members gathered in front of hospitals and Kocani’s city offices begging authorities for more information.

Toshkovski said police have arrested one man, but didn’t provide details on the person’s involvement.

“Deeply saddened by the tragic fire in Kocani North Macedonia, which claimed lives of too many young people,” Marta Kos, the European Commissioner for Enlargement, wrote in a post on X. “My thoughts are with the victims, their loved ones and the whole of North Macedonia.”

North Macedonia is a candidate for EU membership.

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AP writer Derek Gatopoulos contributed from Athens, Greece.