Story highlights Police say tens of thousands were at the protest in Seoul

Demonstrators are angry over an abuse-of-power scandal involving the president

Seoul, South Korea (CNN) South Korean President Park Geun-hye's two apologies have not quelled some Koreans' anger over an abuse-of-power scandal engulfing her administration.

Thousands took to the streets in Seoul on Saturday, calling for Park to step down and blocking a 16-lane highway in the capital. Police said the crowd had 40,000 to 50,000 people; organizers said 100,000 protested.

Park is accused of letting her confidante Choi Soon-sil, who does not hold an official government post, view confidential documents and presidential speeches.

Local media and opposition parties have accused Choi of using her relationship with Park to accumulate millions of dollars in donations to her foundations.

JUST WATCHED South Korean presidential scandal 'unprecedented' Replay More Videos ... MUST WATCH South Korean presidential scandal 'unprecedented' 03:16

Prosecutors issued an arrest warrant for Choi on Wednesday on charges of abuse of power and attempted fraud.

Read More