South Korean President Moon, himself a member of a separated family from the North's eastern port city of Hungnam, said on Monday that the reunions should be sharply scaled up and held on a regular basis and include exchanges of visits and letters.
South Korea's Yonhap Newsreported on Monday that some of the participants were so frail that they spent the reunion in wheelchairs or needed help to stand.
The three-day reunion - the first for three years - will take place in Mount Kumgang resort in North Korea, following a rapid diplomatic thaw between the neighbours.
More than 57,000 South Korean survivors have registered for the family reunions, which usually end in painful farewells.
On seeing him however, there was no hesitation, and the two elderly Koreans embraced each other tightly, both in tears.
Out of almost 56,000 people who applied, a total of 534 South Korean individual were chosen to participate in this program. Another 3,700 exchanged video messages with their North Korean relatives.
She hasn't seen him since he was 4 years old. In total, nearly 300 members of 98 families were able to reconnect in North Korea.
"I've lived this long to meet you", replied the 85-year-old, wiping away tears as she clasped a photograph of her brother in his youth.
"Oh brother, it will be great when reunification happens", she said.
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.
Park fought for the South as a student soldier and was among the allied troops who took over Wonsan in October 1950.
But Jang Hae-won, 89, said he would meet his nephew and niece to reconnect with his parents who passed away in the North and offer his brother's children a glimpse of their father's life.
One 92-year-old South Korean woman wept and stroked the wrinkled cheeks of her 71-year-old North Korean son.
"When I fled home in the war", said Ms. Han, failing to continue as she choked up with emotions. "I wonder whether there's a chance he saw me when I was in Wonsan".
Unofficial reunions can cost about $1500 (NZ$2252), but the process can be faster and is less dependent on the political climate between North and South.
The heart-wrenching reunions, part of three-day event, are the result of an agreement reached in April between North Korean leader Kim Jong Un and South Korean President Moon Jae-in.
About 132,600 Koreans were listed as separated from their families by the end of July. Some experts say warming inter-Korean relations could suffer a setback if the North refuses to accept a US -led call for complete nuclear disarmament, and that is expected to figure into another inter-Korean summit set for next month in Pyongyang.
North Korea is reluctant to accept calls for more reunions.
After 11 hours together over the next three days, the pair will part, nearly certainly never to see each other again, and - unless something changes - they won't even be able to exchange letters.
Another 337 South Koreans will participate in a second round of reunions from Friday to Sunday.