Around 12:30 a.m. local time Friday, the Piper Cheyenne aircraft containing three crew members and one patient departed from airport in Crescent City, California -- about 20 miles south of Oregon.
The plane, which is part of Cal-Ore Life Flight's fleet, was headed for Oakland International Airport, located about 400 miles south.
By 1 a.m., the pilot declared an emergency indicating that there was smoke onboard, said Lt. Wayne Hanson of the Humboldt County Sheriff's Department. Five minutes later, communication with the plane was lost.
Search teams from several agencies including the Coast Guard, Humboldt County Sheriff's Department and Cal Fire fanned the area trying to locate the crash site.
Around 10 a.m. this morning rescue teams found the wreckage just north of McKinleyville, California. But there were no survivors.
The plane crashed in a rural, mountainous area, so no one on the ground was hurt, said
"This is one of the saddest moments in our history," said Cal-Ore Flight in a statement.
"First and foremost, our thoughts and prayers are with the families of the patient and our crew members."
A transport medic, a flight nurse, a patient and the pilot had been onboard.
The company stated that it could not release the identities of the deceased until they receive confirmation from local authorities.