Six people were killed in a fire that tore through a packed nightclub in the northern Serbian city of Novi Sad overnight, police said on Sunday.
Police said the fire appeared to have started in the stage area of the Contrast nightclub during a live performance shortly after 2 a.m. (0000 GMT).
The victims, who were in their early 20s, most likely choked to death after locking themselves in the toilets of the club to escape the fire, the head of the interior ministry's emergencies department, Predrag Maric, told state television.
Some 300-350 people are believed to have been in the club at the time.
Investigative judge Ana Stamenic said 50 people had been taken in by police for questioning, including the owner of the club, and that prosecutors were considering charges of "causing general danger."
Novi Sad mayor Igor Pavlicic said the club had only recently carried out a fire drill and was regularly checked for compliance to safety regulations.
In 2008, eight people died in a fire in the Lounge cafe in Novi Sad and three died in a fire at the city's Putnik hotel the previous year.
"This is a great tragedy," Pavlicic told reporters. "The wounds of past tragedies in Novi Sad have yet to heal, and now we have another."