More than 100 South Koreans left for North Korea on Thursday for their first reunions with relatives they haven't seen for six decades amid lingering tensions on the divided Korean Peninsula.

A total of 82 elderly South Koreans, accompanied by 58 family members, were to arrive on Mount Kumgang, a scenic resort on the North's east coast, later in the day for the reunions with 180 North Korean relatives that will last until Saturday.

Their bus trip across the heavily fortified border comes four days before South Korea and the United States kick off their annual joint military exercises, denounced by the North as a rehearsal for invasion.

The North had demanded that Seoul delay the military exercises until after the reunions end, but it later backed down in their rare high-level talks.

The North's concession paved the way for the two Koreas to stage the reunions for the first time since late 2010, in a rare sign of thawing ties amid Pyongyang's recent conciliatory overture toward Seoul.

South Korea has called the reunions a first step toward improving inter-Korean relations after months of tensions over Pyongyang's harsh war rhetoric against Seoul and Washington.

The South Koreans will meet with their North Korean relatives at 3 p.m. before they eat dinner together, in their first reunions since the 1950-53 Korean War.

Millions of Koreans remain separated because the Korean War ended in a cease-fire, not a peace treaty.

Family reunions are a pressing humanitarian issue on the divided peninsula, as most of the separated family members are in their 70s and 80s, and wish to see their long-lost relatives before they die.

There are no direct means of contact between ordinary civilians of the two countries, which remain divided by a heavily fortified border.

The Thursday-Saturday reunions will be followed by another round of nearly a combined 450 people from both sides.

The reunions are set to end Tuesday, a day after Seoul and Washington begin their joint military exercises meant to heighten their defense posture against possible provocations from North Korea.

South Korea has repeatedly called for frequent family reunions with North Korea. Still, the North has balked at the idea of staging frequent family reunions. (Yonhap)