About 850,000 people joined the candlelight rally at Gwanghwamun and a public square near Seoul City Hall as of 6:30 p.m., according to organizers. Police said 220,000 people gathered as of 5:30 p.m.
The number surpasses 170,000 originally expected by police. Organizers forecast up to 1 million people will turn out.
It is the largest rally to be held in South Korea this century to date. Police said they deployed some 25,000 officers to prevent potential violence.