Four people were killed on early Saturday morning when a small plane crashed at an airport in southern Utah, but it took more than four hours before the wreckage was discovered, local and federal officials said on Sunday.

The accident is believed to have happened at around 1:30 a.m. local time on Saturday when the single-engine Cessna 172 fixed-wing airplane took off from St. George Municipal Airport, located near St. George in Washington County. The aircraft was carrying four young men on board.

But because the airport is not staffed at night and instead uses an automated system, the wreckage of the plane was not discovered until 6 a.m. during a routine security check of the airport's property. The plane was found about 300 yards (365 meters) from the runway, and rescue workers confirmed there were no survivors.

The National Transportation Safety Board (NTSB), which is investigating the cause of the accident, said a security camera at the airport captured the plane flying at a low altitude above the runway before it made a rapid ascent. It was not immediately clear if the video showed the actual crash.

The victims were identified as 28-year-old Colby Hafen, 20-year-old Christopher Chapman, 23-year-old Tanner Holt, and 22-year-old Alexander Metzger. It is unknown if they died immediately upon impact, but officials said they have no reason to believe anyone was alive after the aircraft went down.

The cause of the accident is under investigation.