SEOUL/MUAN COUNTY, SOUTH KOREA -- Air safety experts on Tuesday questioned the placement of an airport embankment into which a South Korean passenger jet slammed after skidding past the end of the runway, resulting in the country's deadliest domestic air disaster.

All 175 passengers and four of the six crew were killed on Sunday when the Jeju Air plane belly-landed at Muan International Airport, ploughed into the sand-and-concrete embankment and burst into a fireball.

What caused the pilot to attempt the landing after declaring an emergency was still under investigation.

But comments in the airport's operating manual, uploaded early in 2024, said the embankment was too close to the end of the runway and recommended that the location of the equipment be reviewed during a planned expansion.

A transport ministry official said on Tuesday authorities would need to check the document before replying to questions.

Experts criticised the positioning of the embankment, which held navigation equipment.

"Unfortunately, that thing was the reason that everybody got killed, because they literally hit a concrete structure," Captain Ross Aimer, the chief executive of Aero Consulting Experts, told Reuters. "It shouldn't have been there."

Meanwhile, police worked to identify victims while impatience rose among families gathered at the airport as they waited for the bodies of their loved ones to be released.

The National Police Agency said it was making all-out efforts to speed up identification of the five bodies still unknown, allocating more personnel and rapid DNA analysers.

The Boeing 737-800's "black box" flight data recorder recovered from the crash site was missing a key connector and authorities were reviewing how to extract its data, but retrieval of data from the cockpit voice recorder has begun, the transport ministry said.

Inspections of all 101 B737-800s operated by South Korean airlines are set to wrap up by Jan 3, though the airport will stay closed until Jan 7, it added in a statement.

Personnel from the US National Transportation Safety Board (NTSB), Federal Aviation Administration, and aircraft maker Boeing have joined the investigations.

On Monday, Acting President Choi Sang-mok ordered an emergency safety inspection of the country's entire airline operation.