As recovery efforts continue, authorities in California have confirmed 20 deaths from a fire that broke out on a boat offering a scuba getaway off the coast of Santa Cruz Island over Labor Day weekend. A total of 39 passengers  — 33 guests and six crew members — were aboard the vessel.

“This is probably the worst-case scenario you can possibly have,” Santa Barbara County Sheriff Bill Brown said. “You have a vessel that's on the open sea, that is in the middle of the night. I mean, it's 3:30 in the morning.”

As of Tuesday morning, CNN reports that only five survivors have been recovered from the wreck, all of them crew members. The operation officially transitioned from a rescue mission to a recovery operation. The cause of the blaze, which erupted on the final day of the trip, is not yet known.

A mayday dispatch provided a glimpse into the events that led to the vessel’s demise. Only the Coast Guard dispatcher can be heard responding to the captain of the boat, who seems to initially report a fire and gives the boat’s location.

“And there's 33 people on board the vessel that's on fire, they can't get off?” the dispatcher responds. “... Roger, are they locked inside the boat?... Roger, can you get back on board and unlock the boat, unlock the door so they can get off?... Roger, you don't have any firefighting gear at all? No fire extinguishers or anything?”

Later in the call, the captain seems to say, “I can’t breathe.”

Ventura County firefighters were able to reach the boat in 15 minutes but by the time they arrived the boat was completely consumed by flames.