The fire was probably caused by the use of pyrotechnic devices "used for light effects at the concert", said Interior Minister Pance 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.

The interior ministry announced that arrest warrants had been issued for four people in relation to the tragedy, and a criminal investigation opened. They did not immediately give further details about those targeted by the warrants.

"According to the information that we have, there are 59 persons deceased of which 35 are identified. Of the identified, 31 persons are from Kocani and four from Stip," Toskovski said.

"The number of wounded, according to latest information up to noon (1100 GMT), is 155 persons who are in hospitals across the country," Toskovski said.

"Preparations are being made to transport people seriously injured in the fire in Kocani to top hospitals in several European countries," the head of North Macedonia's Crisis Centre, Stojanche Angelov, said.

The head of the Kocani hospital, Kristina Serafimovska, told media that the patients being treated there were aged between 14 and 25.

"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, Prime Minister 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," he said.

Videos posted on social networks and shot before the fire showed the use of "stage fountains", which are 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.

Leaders of neighbouring countries offered help.