For the fifth straight weekend, masses of protesters occupied major avenues in downtown Seoul on Saturday demanding the ouster of President Park Geun-hye.

She is suspected of helping in the criminal activities of a secretive confidante who is accused of manipulating government affairs and extorting companies to build an illicit fortune.

Prosecutors investigating the case have indicted her friend, Choi Soon-sil, and are seeking to question the president about her role in the scandal.

For the fifth straight weekend, masses of protesters occupied major avenues in downtown Seoul demanding the ouster of Park, who is accused of helping in the criminal activities of a secretive confidante. (Lee Jin-man/Associated Press)

Choi was indicted along with a former presidential aide on Sunday on charges of colluding with Park to pressure companies to contribute funds to two foundations controlled by Choi.

Park, whose five-year term ends in February 2018, has apologized twice over the affair but is resisting calls for her resignation.

Riot officers stand to block protesters in Seoul on Saturday. (Kim Kyung-Hoon/Reuters)

Even some members of her ruling Saenuri Party have said she should step down, but she would risk losing immunity against prosecution if she did. Meantime, opposition parties are canvassing for support to impeach her.

While the opposition parties control parliament, they would have to garner votes from Park's own party to secure the two-thirds majority needed to pass a motion to impeach her.

How big are the protests?

Mass protests against Park over the past four weekends have been the biggest public demonstrations seen in South Korea since the 1980s.

Saturday's rally renewed what has become a weekly back-and-forth between police and protest organizers, whose crowd estimates have differed widely.

Police said about 270,000 people turned out on Saturday, making it the largest anti-Park rally yet. Organizers estimated the crowd at 1.5 million.

Crowd size estimates by police and organizers differ wildly. (Jeon Heon-kyun/Reuters)

For the police, the aim is to measure the maximum crowd occupying a certain space at any given time so that they could determine the size of police personnel and resources to deploy, according to an official from the Seoul Metropolitan Police Agency, who didn't want to be named, citing office rules.

Han Seon-beom, one of the protest organizers, admits outright that their measurements aren't scientific, but still argues they are more reliable than police numbers.

Organizers seek to track the entire flow of people from the protest's start to its finish. They collect estimates given by counters deployed at different locations to size up the crowds in each area and update the numbers throughout the duration of the protest.

Demonstrates numbered in the hundreds of thousands at least, and organizers say 1.5 million people took to the streets. (Ahn Young-joon/Associated Press)

They try to account for the people on the sidewalks, spaces between buildings and also those moving in and out of nearby subway stations and restaurants, Han said.

The numbers of participants reported by organized groups, such as labour unions, are also put into account.

There are many challenges for counting the number of protesters. The rallies stretch from midday to late niht — some people stay for several hours, others just several minutes. The demonstrators not only gather in open space, but also small alleys and between buildings. Some of them are constantly moving.

Economic turmoil

The political turmoil has exacerbated fraying business confidence in Asia's fourth largest economy, which is already suffering from slowing growth and rising household debt.

"This is a serious problem because companies are delaying all their business decisions due to political uncertainties," Hansung University economics Professor Kim Sang-jo said. "All policymaking seems to be in pause."

South Korean President Park Geun-hye is under fire over allegations that a close friend used her ties to the leader to meddle in state affairs and wield improper influence (Kim Hong-Ji/Reuters)

South Korea's export-driven firms are also worried by the potential impact of U.S. president-elect Donald Trump's protectionist stance on trade issues.

The Bank of Korea is due to publish its next business confidence survey next week, but a consumer confidence survey released on Friday showed South Koreans were at their most gloomiest in 7 1/2 years.