The red-shirt anti-government protests in Bangkok have taken a bloody turn.

But it's not a case of violence - thousands of protesters are voluntarily giving blood, which will be splashed across the entrance to the prime minister's office, in what protest leaders say will be a symbolic spilling of blood for democracy.

In the latest development in the four-day protest, supporters of former Prime Minister Thaksin Shinawatra are continuing to call for fresh elections, saying the current government is illegitimate.

[Jatuporn Prompan, Protest Leader]:
"It is to remind Abhisit Vejjajiva's conscience that he takes power illegitimately and stays in the post longer than expected. He hasn't had the right to be prime minister since the beginning, therefore, whether or not to dissolve the parliament - it is up to you (Abhisit). People will continue to intensify their non-violent protests."

Protest organizers are aiming to collect 1 million cubic-centimeters of blood, in a nation that has known actual bloodshed in its recent political history.

[Boonpeng Nammata, Protester]:
"We have to collect blood to be united. One million, two or three million people should unite, giving blood for democracy and justify Thailand."

Police say the crowds of protesters, which peaked at around 150,000 on Sunday, have declined to around 70,000.

And as the crowds shrink, Thai Prime Minister Abhisit Vejjajiva stands firm, saying on Monday the government would not meet protester demands for a dissolution of parliament.