SEOUL: South Korea is seeing its biggest wave of street demonstrations in decades, but nobody is sure how many people are taking to the streets each week.

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.

The rally renewed what has become a weekly back-and-forth between police and protest organisers, whose crowd estimates have differed widely. Police said about 260,000 people turned out on Saturday, while organisers saw it at 1.3 million.

There are many challenges for counting the number of protesters. The rallies stretch from midday to late night — 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.

A look at how police and protest organisers size the crowds at protests, and also how South Korean scientists and a technology company are exploring new ways to more accurately measure the number of protesters: