Tens of thousands of South Korean women on Saturday angrily urged the government to crack down on secretly-filmed spycam pornography in one of the biggest-ever female-only protests in the country.

So-called spycam videos have become increasingly common in the South, where men caught secretly filming women - in schools and workplaces, toilets and changing rooms - make headlines on a daily basis.

Distributing pornography is illegal in South Korea, but such videos are widely shared on porn sites and Internet chatrooms or used in adverts for websites promoting prostitution and gambling.

"Those men who film such videos! Those who upload them! Those who watch them! All of them should be punished sternly!" the protestors chanted in unison at the rally held in central Seoul.

Many held banners reading "My life is not your porn" and "We're humans, not a sexual object for your sick fantasy".

Organisers said around 55,000 women took part in the demonstration but police put the estimate at about 20,000.