A medical helicopter crashed into the ocean off Santa Catalina Island on Wednesday night, killing two people aboard and leaving one missing as search efforts continued into Thursday.

The Airbus H-135 operated by REACH Air Medical Services was transporting a patient from the island to the mainland when it went down near Pebbly Beach, close to Avalon, shortly after 7:50 p.m. PDT. The aircraft had arrived on the island earlier that evening after departing from Oceanside.

Los Angeles County Fire Department personnel and U.S. Coast Guard crews responded quickly, recovering four of the five people from the water. Two were pronounced dead at the scene. The pilot and a flight nurse were identified among the fatalities. Two survivors were transported to hospitals on the mainland in stable condition.

The helicopter submerged in approximately 240 feet of water about 22 miles off the Los Angeles County mainland. The National Transportation Safety Board is leading the investigation into the cause, which remains undetermined. The Coast Guard deployed boats, helicopters, divers, and a remotely operated vehicle for the ongoing search for the missing person, believed to be the patient.

REACH Air Medical Services stated it is cooperating with authorities and gathering information while expressing concern for those involved. Los Angeles County Supervisor Janice Hahn noted on social media that search and rescue operations were underway.

The incident occurred as the helicopter prepared to depart the island for additional medical care on the mainland. No further details on the victims or the precise circumstances of the crash have been released.