South Koreans leave for North Korea to take part in family reunions with their North Korean family members. Picture: Korea Pool/Yonhap via AP

Seoul, South Korea - Nearly 90 South Korean families crossed the heavily fortified border into North Korea on Monday to be reunited with elderly relatives they had not seen since being separated in the chaos of war nearly seven decades earlier.

Brothers, sisters, cousins, nephews and nieces cried and embraced each other in the first family reunions to take place in three years, a symbol of thawing ties across the Korean Peninsula.

Some relatives couldn't even recognise each other, but that wasn't a problem for 88-year-old Kim Byung-oh and his 81-year-old North Korean sister Kim Soon-ok who were separated while still at school.

"I haven't slept a wink since being selected for this family reunion," Byung-oh said as he met his sister, according to brief pool reports supplied by South Korean reporters.

"Blood ties don't disappear, even after all this time," Soon-ok replied. "You really look exactly like me."

Soon-ok showed her brother an old photograph of herself at medical school and said she had worked as a doctor. "I lead a respected life in Pyongyang," she said.

Byung-oh said he had worked as a high school headmaster until retiring 10 years before, adding that it was an honour to see his sister had done so well.

"Oh brother, it will be great when reunification happens," she said. "Let reunification happen and let's live together for even just one minute before we die," she said tearfully.

After 11 hours together over the next three days, the pair will part, almost certainly never to see each other again, and - unless something changes - they won't even be able to exchange letters.

The reunion programme began in 1985, stalled, then got underway properly at the turn of the millennium. In all, more than 17,000 South Koreans families have taken part in 20 reunions since then, with a few thousand more taking part in a brief programme of video linkups.

But North Korea's suspicion of any outside influence means that many tens of thousands more have been denied the chance to meet: more than 130,000 South Koreans have registered as members of divided families since the programme began, but more than half of them died before getting to meet their relatives again. Of those still on the waiting list, more than 12,000 are over 90 years of age.

For many participants these reunions represent the first news they have had of their relatives in nearly seven decades.

"It is a shame for both governments in the South and the North that many of the families have passed away without knowing whether or not their lost relatives were alive," South Korean President Moon Jae-in told a meeting with presidential secretaries Monday.

Moon is himself a member of a divided family: His parents fled on a ship from the North Korean port of Hungnam in December 1950, and he accompanied his mother to meet her younger sister during an earlier family reunion in 2004.

"Expanding and accelerating family reunions is a top priority among humanitarian projects to be carried out by the two Koreas," he said.

The South Korean families, 89 applicants usually with two or three relatives accompanying them, were bused across the border on Monday morning to the North Korean resort of Mount Kumgang.

Many were war refugees who fled south during the war, leaving relatives behind. Some crossed in wheelchairs pushed by relatives and Red Cross volunteers: The oldest is a 101-year-old man.

During the three years since the reunions were last held, the North tested three nuclear weapons and many missiles, some of which could potentially reach the continental United States. But this year has seen a pause in the nuclear and missile program and an attempt, led by President Donald Trump and South Korea's Moon to find a diplomatic path out of the crisis.

North Korean leader Kim Jong Un agreed to restart the reunions at a summit with Moon in April. Trump then met Kim in Singapore in June, although there has since been little indication that the North Koreans are genuinely willing to abandon their nuclear program.

As the meetings got underway Monday, North Korean sisters Kim Gyong Sil and Kim Gyong Yong waited nervously for their mother to arrive. Seventy-two and 71, respectively, they were dressed in violet hanboks, the Korean traditional dress, and as she approached they stood up, bowed and burst into tears.

They cried loudly for several minutes, before finally settling into conversation. Their mother Han Shin-ja, 99 years old, did not let go of their hands the entire time they were talking.

But the reunions are often also tinged with frustration, with many North Koreans determined to publicly demonstrate their allegiance to the regime, out of genuine loyalty or just fear. Some have even sung propaganda songs in the past, something that can cast an understandable chill over proceedings.

Indeed, 84-year-old Cha Je-keun soon got into an argument with his 50-year-old nephew Cha sung Il. Agreeing that the two nations should be reunified, the younger man exclaimed: "American bastards should be expelled," adding: "Look, uncle, they are not carrying out the Singapore agreement."

South Korean Je-keun tried to explain that the Korean War took place because North Korean leader Kim Il Sung invaded on June 25, 1950.

"That's a lie," his nephew said, parroting North Korean propaganda. "American bastards waged the 6.25 war. We fought on our own."

"Yeah, that was good," Je-keun answered with a smile, ending the quarrel.

In the last round of reunions in 2015, Kim Hyun-sook met her North Korean daughter and granddaughter, but felt they couldn't speak freely in front of her.

"What they told me was shaped by the communist regime," the 90-year-old said. But she added it was still an emotional, if bittersweet, moment.

"It was hard to say goodbye. In fact, meeting them for that little moment made me miss them more ardently than before," she said in an interview. "I really wish I could see them once more while I am alive, but I can't go to a reunion event again because I have already been once."

A second round of reunions involving a further 83 families will take place from Friday to Sunday. While South Korean choose participants through a computerized lottery, experts say North Koreans select candidates based on their perceived loyalty to the regime.