South Korean authorities said on Monday they will change the concrete barriers used for navigation at airports around the country after the Jeju Air crash that left 179 people dead.

The Boeing 737-800 was flying from Thailand to Muan, South Korea, on December 29 carrying 181 passengers and crew when it belly-landed at Muan airport and exploded in a fireball after slamming into a concrete barrier.

It was the worst-ever aviation disaster on South Korean soil.

"Improvement was deemed necessary including the localizer and its foundations for a total of nine facilities across seven airports, including Muan airport," the land ministry said in a statement.

The changes would also apply to international airports in the cities of Jeju and Gimhae.

South Korean and US investigators are still probing the cause of the crash, which prompted a national outpouring of mourning with memorials set up across the country.

Attention has focused on several possible causes but questions have been raised about why the concrete barricade, known as a localizer and used to help planes navigate their landings, was at the end of the runway.

The barrier at Muan airport was blamed for exacerbating the crash's severity.

The ministry said it would finalize plans to adapt the localizers by the end of January, with the aim of "completing upgrades within this year."

The investigation was further clouded on Saturday when the transport ministry said the black boxes holding the flight data and cockpit voice recorders for the crashed flight stopped recording four minutes before the disaster.

Authorities have raided offices at Muan airport, a regional aviation office in the southwestern county, and Jeju Air's office in the capital Seoul as the probe continues.

The land ministry added that Muan airport's closure period had been extended until 19 January.