(CNN) A group of mostly elderly South Koreans crossed into North Korea Monday to reunite with family members many haven't seen nor heard from since the Korean War broke out 68 years ago.

The reunions are the first since 2015, agreed to under the Panmunjom Declaration signed by South Korean President Moon Jae-in and North Korean leader Kim Jong Un during an historic summit earlier this year.

More than 57,000 people had been hoping to take part in the reunions, but of those only 93 families were selected, four of whom had to pull out at the last minute due to health reasons.

More than 60% of those seeking reunions are over 80 years old, and are being accompanied on the bus trip north by their children and other relatives.

Long awaited reunions

The South Koreans gathered Sunday at the Hanwha resort hotel, in Sokcho, south of the demilitarized zone (DMZ) which separates the two Koreas, where medical checks were carried out and participants were warned about nuances of visiting North Korea. They're told to avoid saying anything that could be misconstrued, or considered insensitive north of the border.

Participants were applauded by Red Cross workers as they arrived, some in wheelchairs, passing under banners reading "We sincerely congratulate the reunions of the separated families!"

In the hotel there was an air of excitement and tension as they prepared to meet husbands, wives, brothers, sisters and children who are now only vague memories, their faces blurred by time.

They then registered their names and were invited to take a professional family photo in a corner of the lobby. It was then framed for them so they could then take it to North Korea as a gift.

South Korean participants of the inter-Korean family reunions stand for the national anthem as they undergo a briefing on the eve of the departure for North Korea, at a hotel resort in Sokcho on August 19, 2018.

Lee Keum-seom, who was preparing to see her son for the first time since he was four years old, said she had prayed for him to have a long life so the pair -- now 92 and 72 respectively -- could reunite.

"(My family) in North Korea didn't live long so I prayed for my son's health," she said.

She felt nervous about meeting her now elderly son, after only knowing him as a small child, unsure about where to start catching up on a lifetime spent apart.

"What shall I ask?" she said. "Oh, I should ask him what his father told him about me. His father must have told him about how we got separated and where our house used to be. I should ask him about that."

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Park Kyung-seo, president of the South Korean Red Cross, told CNN that while he was overjoyed to be assisting in family reunions, the small number of those taking part was a "human tragedy."

"I share fully with the disappointment of those who are not selected so I am trying with North Korean partners to try and find other solutions, huge numbers are waiting, the numbers are very much limited," he said.

"Imagine 73 years long without knowing whether their family members are still alive or passed away -- no news at all. The agony and anger, that's an unthinkable human tragedy."

A convoy of buses carrying participants of an inter-Korean family reunion makes its way through the Demilitarized Zone (DMZ) towards North Korea.

Ahn Seung-chun was headed to North Korea to see family members she's never met. "I applied to see my older brother," he said. "But he passed so I'll never see him now."

"I'm going to see my nephew and my brother's wife," she added. On one hand, I'm sad that I won't see my brother. But on the other hand, I'm happy to meet the nephew. At least I will be meeting a fruit of my father."

Dokgo Ran was separated from his entire immediate family during the Korean War, and never expected to see them again.

"The Red Cross asked around for my family and helped me reunite. I'm grateful," he said.

Dozens of elderly and frail South Koreans set off for North Korea on August 20 to meet relatives for the first time since they were separated nearly seven decades ago by a war that divided the peninsula and their families.

Bittersweet process

In the decades since the Korean War, the Red Cross has reunited many families but thousands of others have missed out.

As family members age, each delay adds to fears that they'll no longer be around to finally meet with their long lost relatives. More than 75,000 applicants have already passed away since the reunion process began.

One protester attended Sunday's event to voice his elderly father's case for a reunion, after the man was unlucky this round.

"I don't know when he will die. He is beginning to show signs of dementia. Before he loses everything, he wants to go too," Kim Seong-jin said. "But all he can do is to watch through television each time and get hurt."

Amid all the joy and happy scenes on both sides of the border this week, this is the reality for most whose families remain split by the Korean War.

"My father is all alone here in the South. Can you imagine how much he misses his family?" Kim said. "He wants to hear the news of his hometown before he dies."

Lee Keum-seom undergoes a health check as she prepares to head to North Korea to reunite with her long-lost son.

Legacy of war

The pain felt by the families split by the Korean War is one of the most visible legacies of the conflict which, 68 years after it began, still hasn't technically ended

An armistice agreement which paused fighting in 1953 never became a formal peace treaty, and small skirmishes have happened since on either side of the heavily fortified DMZ, even as North Korea has built up its nuclear armaments and the US has maintained a heavy military presence in the South.

Officially ending the war was a key element of the Panmunjom Declaration, and both North and South have said they are continuing to work towards that goal, even as negotiations between Pyongyang and Washington appear to have stalled.

North Korean state media called on the US to agree to an official end to the war last week, saying it was a "preliminary and essential process to pave the ground for detente and permanent peace on the Korean Peninsula."

"The U.S. should implement phased and simultaneous measures, like the end-of-war declaration, to build mutual trust and make a breakthrough in the security of the world," state media Rodong Sinmun said in a commentary.

The Unified Korea delegation enters the stadium during the opening ceremony of the Asian Games 2018 at Gelora Bung Karno Stadium on August 18, 2018 in Jakarta, Indonesia.

As well as the family reunions, Saturday saw the fulfillment of another commitment made by Moon and Kim, as a joint Korean team marched in the opening ceremony of the Asian Games in Jakarta, Indonesia.

That move came after a unified Korean team took part in the Winter Olympics in Pyeongchang, South Korea earlier this year, negotiations over which helped kick start a breakthrough in North-South relations and lead to the current detente on the Peninsula.