A fire tore through a nightclub in North Macedonia early on Sunday, killing 59 people, apparently after on-stage fireworks set the place ablaze, authorities said, announcing that four people had been arrested.

They said 155 injured people had been taken to hospitals across the country, 18 of them in critical condition. Some of the serious cases were to be taken to other European countries for treatment.

The blaze started in the Club Pulse in the eastern town of Kocani around 3am, as the place was packed with more than 1,000 mostly young fans attending a concert by a a popular hip-hop duo called DNK.

"Initially we didn't believe there was a fire. Then there was huge panic in the crowd and a stampede to get out," one young woman at the concert told local media outside a hospital in the capital Skopje.

Kocani is 100 kilometers east of the capital Skopje. North Macedonia is landlocked and borders Serbia to the north, Kosovo to the northwest, Bulgaria to the east, Greece to the south, and Albania to the west.

Fire crews and paramedics responded quickly and "tried to resuscitate people., but it wasn't enough", said a woman waiting at hospital for a friend being treated for burns to his hand.

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 added. 

The interior ministry announced that arrest warrants had been issued for four people in relation to the tragedy, and a criminal investigation opened. 

"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 said patients being treated were aged between 14 and 25.

"70 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'

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

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. 

Leaders of neighboring countries offered help.

European support

Bulgarian Prime Minister Rossen Jeliazkov spoke on Facebook of the fire being "a huge human tragedy" and offered to have his air force fly some of those injured to medical facilities in the Bulgarian capital Sofia and the city of Varna.

Greek Prime Minister Kyriakos Mitsotakis sent "heartfelt condolences to the people of North Macedonia for the lives lost in the tragic fire".

Albanian Prime Minister Edi Rama said he was "at a loss for words" and expressed readiness "to provide any assistance that may be needed".    

There were also messages from parts of the EU, which North Macedonia has ambitions to join.

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