The outlook for next month's sporting extravaganza has brightened since North Korea confirmed its participation, lifting security concerns over the South's nuclear-armed neighbour.
The North has agreed to send an unknown number of athletes to the Games, expected to be accompanied by a high-level delegation, supporters, observers and an art troupe.
South Korean freestyle figure skater Park Hee-Jin raised the flame high before a crowd hundreds who were gathered in the capital's Sangam district in a ceremony held just weeks before the event on February 9-25.
Fans unfurled banners wishing the Olympics success accompanied by the rousing sound of traditional Korean drummers, while others took pictures with their phones.
The skater, who took part in the Sochi Winter Olympics' qualifying rounds, then passed the flame to the next of more than 600 torchbearers who will lead it on a 103 km (64 mile) journey around the capital until Tuesday.
It will arrive late Saturday at the main entrance to Gyeongbokgung Palace, the grandest of Seoul's historic sites, and will be carried in a sedan chair as hundreds of participants in traditional court costumes re-enact a royal outing.
The torch was relayed by 16 runners to Korean football star Cha Bum-Kun near the Sangam World Cup Stadium, a venue for the 2002 FIFA World Cup.
"Go Pyeongchang, Go Korea football", former Bundesliga player Cha said as he set off, with fans chanting his name.
The flame arrived in South Korea on November 1, 100 days ahead of the opening ceremony for the 2018 Pyeongchang Winter Games.
It has travelled throughout the country, relayed by a who's who of Korean sports and entertainment stars including Kim Yuna, who won the ladies singles figure skating at the 2010 Vancouver Olympics and the silver in the same discipline at the 2014 Sochi Olympics.
Speed skater Lee Sang-Hwa, who will be aiming for a record-equalling third Olympic gold in the women's 500m in Pyeongchang, former US major league baseball pitcher Park Chan-Ho and Choo Shin-Soo, who plays for baseball team Texas Rangers, also held the torch.
Overall, some 7,500 torchbearers will have taken part in the relay, covering more than 2,000 kilometers.