Huge rallies have been held across South Korea for what are thought to be the largest protests so far demanding President Park Geun-hye steps down.
Ms Park is accused of allowing her friend, Choi Soon-sil, to manipulate power from behind the scenes.
The president has apologised twice, but has so far resisted calls to resign.
Organisers said 1.5 million were in Seoul, and another 400,000 in other regions of the country. Police put the turnout in the capital at 270,000.
About 25,000 officers were deployed in Seoul but there were no reports of violence.
The protests, which began five weeks ago, were the largest in South Korea since pro-democracy demonstrations of the 1980s.
Those attending on Saturday came from a cross-section of South Korean society, with farmers, Buddhist monks and university students all involved.
"I was watching the news and thought this cannot go on - people really want her to step down but she hasn't," one of the protesters, Kwak Bo-youn, told Reuters.
"This is the second time for me to the protests, but the first time for my husband and kids."
Ms Park, whose approval rating has dropped to 5%, apologised earlier this month for putting "too much faith in a personal relationship", and has pledged to co-operate in an official investigation into the scandal.
South Korea's constitution does not allow a sitting president to be prosecuted, and Ms Park has 15 months left in her term.
But now that prosecutors have directly linked her to the scandal, it is possible she could be impeached for breaking the law.
Prosecutors are expected to bring charges against Ms Choi, along with two former presidential aides. She was arrested earlier this month.
Ms Choi is accused of trying to extort huge sums of money from South Korean companies, and suspected of using her friendship with Ms Park to solicit business donations for a non-profit fund she controlled.