By Yoonjung Seo, Gawon Bae and James Legge, CNN

Seoul, South Korea (CNN) — Scores of people were killed on Sunday when a passenger jet crash-landed at an airport in southwestern South Korea, with the aircraft careening down the runway on its belly before bursting into flames.

Just two of the 181 people on board the plane survived, after the deaths of 179 people were confirmed, according to the local fire department. The two crew members were pulled alive from the crash site.

It is the deadliest aviation disaster to hit South Korea since 1997, when a Korean Airlines Boeing 747 crashed in the Guam jungle, with the loss of 228 lives.

What happened?

Jeju Air flight 7C 2216 from Bangkok was carrying 175 passengers and six crew when disaster struck at the airport in Muan county, on the country’s southwestern tip, just after 9 a.m. local time Sunday (7 p.m. ET Saturday).

Footage of Sunday’s crash broadcast by multiple South Korean news outlets showed the plane sliding on its belly at high speed, hitting an earthen embankment and erupting in a fireball.

Neither the back nor front landing gear was visible in the footage – broadcast by networks including YTN, JTBC and MBC – as smoke poured from the back of the sliding aircraft.

Firefighters were later seen using water cannons to extinguish the blazing wreckage of the aircraft, which was listed as a Boeing 737-800 on flight-tracking site FlightAware. Several parts of the aircraft were also seen strewn across the runway.

The victims include 84 males, 85 females, and 10 people whose gender could not be determined, according to the South Jeolla Fire Service. Both of the survivors were crew members, one male and one female, according to the rescue team.

Two Thai nationals were among those on board, according to the South Korean Land Ministry. All the other passengers were South Korean.

What caused the accident?

Experts told CNN that the plane’s undercarriage – specifically, the wheels used for takeoff and landing – appeared not to have fully deployed before landing. But what caused this failure to deploy is still unclear.

Aviation analysts said more evidence is needed before South Korean authorities can definitively pinpoint what might have caused Sunday’s crash, including speculation from local officials about a possible bird strike prior to the crash landing.

The comments came after Lee Jeong-hyun, the head of the Muan Fire Department, briefed the media that the cause was “estimated to be the occurrence of a bird strike or bad weather.” Footage of the crash showed clear skies at the time.

David Soucie, former Federal Aviation Administration safety inspector, said that “speculation is the worst enemy of an investigator.”

“In fact, that’s why it’s so protected when there is an aircraft accident investigation, the information is protected. They’re not supposed to be making any speculation about this type of thing,” Soucie told CNN’s Paula Newton.

Aviation industry consultant Scott Hamilton echoed Soucie’s concerns and urged South Korean authorities to “stop making declarative statements” at this stage.

Sunday’s crash is “very perplexing” given that both the aircraft and carrier have a strong safety record and flying conditions were excellent, an aviation journalist said.

The Boeing 737-800 is one of the most widely used aircraft in the world and each one is used for about four or five flights per day, Geoffrey Thomas, editor of Airline News, told CNN’s Paula Newton.

“It is the most reliable aircraft in the world, and it’s been in service for 20 years,” he said. “Everybody knows how it works. And it works really, really well. And the maintenance done in [South] Korea is as good as it gets around the world.”

“It’s a little bit unclear whether or not the undercarriage collapsed on landing or whether the undercarriage was not deployed at all. This is a really serious issue that obviously investigators will be very much focused on,” Thomas added.

He added “it is perplexing” that the crash happened, given it was landing under dry and sunny conditions at a good airport.

US aviation giant Boeing has had a turbulent time in recent years, including two 737 Max crashes, a tragedy for which the company agreed to plead guilty to deceiving the Federal Aviation Administration during the certification process for the plane.

However, analysts have described the Boeing 737-800 — an earlier and different model to the Max — as a reliable workhorse of the skies with an extremely strong safety record.

Jeju Air’s chief executive said the aircraft had shown “no signs of issues” prior to Sunday’s accident.

“At this time, it is difficult to determine the cause of the accident, and we have to wait for the official announcement of the investigation by the relevant government agency,” Kim Yi-bae said during a press briefing at the airport.

Where is the investigation focused?

Officers from the national Incident Investigation Committee had arrived to look into what caused the accident.

According to a briefing from the Land Ministry, the control tower had instructed the pilot to change course to land in the opposite direction, to avoid the potential bird strike. The pilot followed the instructions.

Approximately one minute later, the pilot made a mayday call to the tower. The landing attempt occurred approximately two minutes after the mayday call, according to the ministry. Authorities are continuing their investigation.

The “black box” flight data recorder has been recovered by the accident investigation committee while the voice recording device has not been recovered yet, officials from the ministry said.

The flight data recorders or so-called “black boxes” offer aviation safety investigators critical facts when piecing together an incident.

More than 700 personnel from the police, military, and coast guard have been mobilized for on-site response efforts, the ministry added.

What are the authorities saying?

South Korea’s acting president said the site of Sunday’s plane crash has been declared a special disaster zone as he vowed a full investigation into what caused the deadly disaster.

“We will concentrate all resources on recovery and support for the victims. All necessary resources are being mobilized, and a special disaster zone has been declared,” Choi Sang-mok said in a statement.

Choi, who travelled to the crash site on Sunday, extended his “heartfelt condolences to the bereaved families” and pledged to make every effort to manage the aftermath of the incident and prevent similar accidents in future.

The tragedy comes only two days into Choi’s acting presidency, the latest chapter in a time of political chaos in South Korea.

The country’s current president, Yoon Suk Yeol, was stripped of his powers by parliament two weeks ago following a short-lived martial law order that plunged the country into political disarray. He is currently suspended while a top court decides his fate.

Han Duck-soo, the man who stepped in to replace Yoon as acting president, was impeached by parliament on Friday, meaning Choi – the finance minister and deputy prime minister – stepped in for him.

What has the plane’s maker said?

Boeing extended its condolences to those who lost loved ones in the crash.

“We are in contact with Jeju Air regarding Flight 2216 and stand ready to support them,” Boeing said in a short statement posted to its X account.

“We extend our deepest condolences to the families who lost loved ones and our thoughts remain with the passengers and crew,” the company added.

The US aviation giant has had a turbulent time in recent years, including two 737 Max crashes, a tragedy for which the company agreed to plead guilty to deceiving the Federal Aviation Administration during the certification process for the plane.

However, analysts have described the Boeing 737-800 as a reliable workhorse of the skies with an extremely strong safety record.