At least 15 people are dead after the roof of a Santo Domingo nightclub collapsed early Tuesday, according to Dominican Republic police.

It’s not clear what caused the roof of the Jet Set nightclub, a renowned club in the National District, to collapse.

The disaster unfolded during a performance by merengue singer Rubby Perez, local media reported.

There were 101 ambulance transfers to different hospitals, and search and rescue efforts are underway, Juan Manuel Mendez, the nation’s director of Emergency Management Operations, said in an update on Instagram around 8 a.m. The number of those hospitalized may be higher as multiple people may be transferred by an ambulance at a time.

“We are still working, searching for people in the rubble. We presume that many of them are still alive, that’s why the authorities here with their teams will not stop until we find the last person in that rubble,” Mendez said in a video shared on the Dominican Republic National Police Instagram page.