Hundreds of thousands rallied in central Seoul on Saturday for a fifth week of protests against President Park Geun-hye, in the largest ongoing series of demonstrations in the country since the 1987 movement to democratise South Korea.

Park's presidency has been rocked by allegations that a close friend used her ties to the leader to meddle in state affairs and wield improper influence. Prosecutors investigating the case have indicted her friend, Choi Soon-sil, and are seeking to question the president about her role in the scandal.

Organisers said 800,000 people had gathered early on Saturday evening and expected a total of 1.5 million people to join by the end of the night. Police declined to give an estimate of the crowd size but said 25,000 personnel had been dispatched to police the protest.