A party at a warehouse in Oakland turned deadly Sunday after a fire began spreading through a crowd of people. At least 30 people died in the blaze, according to firefighters.

"We anticipate the number of victims will rise and it will increase," Alameda County Sheriff's Sgt. Ray Kelly told reporters at a press conference on Sunday. "This is very hard work, and it's very slow, and it definitely has taken a toll on the first responders. We have people around the clock, and we will be here for days and days to come."

Kelly added that only of the burned-down structure has been searched so far. Rescue workers still have a lot more work to do in the coming days.

Lamenting the dead, Kelly, an experienced fire chief, was shocked at the number of victims firefighters found during their rescue efforts. "That is an astronomical number," Kelly noted. "We're really starting to get deeper into the building, and as we do that, we continue to find more victims."

Firefighters will work day and night to get the job done, said Oakland Battalion Fire Chief Melinda Drayton:

"Within 12 hours we made it through one fifth of the building," she explained. "This will be a long and arduous process, but we want to make sure we are respecting the victims, their families, and our firefighters' safety to work slowly and carefully through the building," she said.

Authorities are holding off on identifying the victims publicly. DNA evidence still needs to be acquired and analyzed because the bodies were so badly charred. Only after notifying the families of the deceased will the police release the names of the victims.

Grief-stricken, the Mayor of Oakland told NBC News on Sunday that “the level of devastation” at the scene was unbelievable. "The magnitude of loss for this community and for these families is unspeakable," she stated. "Our job right now is to stay focused on that as our priority."