SEOUL, South Korea (AP) — For the fourth straight weekend, masses of South Koreans are expected to descend on major avenues in downtown Seoul demanding an end to the presidency of Park Geun-hye, who prosecutors plan to question soon over an explosive political scandal.

Police expect about 50,000 protesters to turn out on Saturday near City Hall and a boulevard in front of an old palace gate.

It will be the latest in a wave of demonstrations calling for the ouster of Park, who critics accuse of undermining the country's democracy by allegedly allowing a secretive confidante to manipulate power from the shadows and amass an illicit fortune.

Prosecutors are planning to formally charge Choi by Sunday and also seeking to question Park in the next few days.