KOCANI, Republic of North Macedonia — A fire tore through an overcrowded nightclub packed with mostly young people in North Macedonia early Sunday, killing 59 people, apparently after on-stage fireworks at a hip-hop concert set the venue ablaze, authorities said.

Some 155 people who were injured in the inferno had been taken to hospitals across the country, 22 of them in critical condition, officials said. Some of the more serious cases were taken to hospitals in other European countries.

Interior Minister Pance Toskovski said that more than 20 wounded and three of those killed in the fire were minors.

"At the time of the event around 500 people were inside, while 250 tickets were sold," he said.

The blaze started in the Club Pulse in the eastern town of Kocani, which was packed with mostly young fans attending a concert by a popular hip-hop duo called DNK.

"The fire started around 2:30 am (0130 GMT), the sparklers that were on stage ignited the styrofoam on the ceiling. I heard an explosion and the roof collapsed," one young person who was inside for the concert told local media.

"We all rushed to get out, we all ran towards one door that was for both entry and exit," they were quoted as saying.

Another, a young woman waiting outside a hospital in the capital Skopje for a friend being treated for burns, said: "Initially we didn't believe there was a fire. Then there was huge panic in the crowd and a stampede to get out."

The fire was probably caused by pyrotechnic devices "used for lighting effects at the concert," said Toskovski, who visited the scene with Prime Minister Hristijan Mickoski.

"Sparks caught the ceiling, which was made of easily flammable material, after which the fire rapidly spread across the whole discotheque, creating thick smoke," Toskovski said.

At a later press conference Toskovski said that the authorities were investigating whether "corruption" and "bribery" were linked to the deadly nightclub fire.

"This company does not have a legal license for work," he said, referring to the club. 

"This license, as many other things in Macedonia in the past, is connected with bribery and corruption. In this case, those involved in illegal issuance of license have names and will be held responsible," he added.

More than 20 people were under investigation over the blaze, 15 of whom were in police custody, while others were in hospital, he said.

Among the suspects are the two members of the band, an owner of the club and organisers, among others.

A former director of the rescue services and a state secretary at the economy ministry were among those detained, he said.

The head of the Kocani hospital, Kristina Serafimovska, told media that "most of the dead unfortunately suffered injuries from the stampede that occurred in the panic while trying to exit".

"Seventy of the patients have burns and carbon monoxide poisoning," she said.

One of the members of the DNK duo that had performed, Vladimir Blazev, had burns to his face and needed assistance breathing, his sister told local media outlets.

 'Very sad day' 

"This is a difficult and very sad day" for the country, Mickoski wrote on his Facebook account. "The loss of so many young lives is irreparable, and the grief of their families, their loved ones and their friends is immeasurable."

The government proclaimed a seven-day mourning period and ordered flags lowered.

"A decision will also be made on an urgent and extraordinary inspection of all nightclubs, discotheques and restaurants that organise parties," the government said in a statement.

Pope Francis sent prayers to the victims and survivors and wished "the families of the dead, mostly young people, the expression of his deep condolence," the Vatican said in a message addressed to the bishop of Skopje, Kiro Stojanov.

Videos posted on social networks and shot before the fire showed there were "stage fountains" set up -- a type of indoor fireworks used during performances. 

Other videos published by media showed huge flames emerging from the building, a two-storey white structure in Kocani, a town with 30,000 residents.

An AFP photographer in the town saw military medical vehicles arrive to reinforce staff at the local hospital tending to some of the injured.

As the day unfolded, the leaders of neighbouring countries sent condolences.

Many of the patients in serious condition were transferred to other countries like Bulgaria, Greece, Serbia and Turkey. 

The EU's foreign policy chief, Kaja Kallas, said on X that she was "deeply saddened about the tragic fire" and that "the EU shares the grief and pain of the people of North Macedonia".