Thousands of South Koreans have taken to the streets of the capital, Seoul, to demand the resignation of President Park Geun-hye over a corruption row.
A long-time friend, the daughter of a cult leader, is accused of undue influence over the president.
Choi Soon-Sil is alleged to have pushed businesses to donate millions of dollars to foundations she controlled, helped choose presidential aides, and even picked the president’s clothes.
Ms Park apologised on TV on Friday.
Ms Park was close to tears as she addressed the nation, and said the scandal involving her confidante Ms Choi was “all my fault”.
The president admitted that she had let Ms Choi edit her speeches.
Ms Choi was arrested on Thursday and charged with fraud and abuse of power.
Some 40,000 demonstrators were expected to attend the rally in central Seoul, watched over by 20,000 police officers. Water cannon are in evidence on the capital’s streets.
Organisers say that as many as 100,000 may join the protest.
Dozens of police buses are parked by City Hall, and near a square which will be closed to stop protesters marching on the Blue House, the president’s official residence.
Smaller protests have taken place every day in recent weeks, as calls grow for Ms Park to step down.
The president has denied media speculation that she took part in “shamanist rituals” at the Blue House, and promised to accept an investigation into her actions.
The affair has left Ms Park with an approval rating of just 5%, the lowest ever for a sitting South Korean president.
The opposition has demanded that she either resign, or accept a prime minister chosen by Parliament as her number two.
