A fire at a popular nightclub in Istanbul, Turkey killed 29 people and injured at least one person Tuesday.

Istanbul Governor Davut Gul said the fire at the Masquerade nightclub happened while it was undergoing renovations. Governor Gul said the victims were believed to be involved in the renovations.

The nightclub was located on two basement floors of a 16-story residential building in downtown Istanbul. The fire engulfed both floors of the nightclub and had reached the building’s third floor before firefighters brought it under control.

Istanbul Mayor Ekrem Imamoglu told reporters the club’s managers had not applied for a permit to conduct renovations or construction work at the site. At least six people have been detained for questioning in connection with the fire, including club management and one person in charge of the renovations.

Video footage of the fire shows firefighters carrying at least one person from the scene on stretchers.

The Masquerade had been closed to the public while the renovations were underway.

The Masquerade website said it would be closed from March 10 to April 10 “due to our new design renovation.” It can host up to 4,000 people with DJ performances and stage shows several times a week, it says.