Tens of thousands of pro- and anti-government demonstrators gathered for rival rallies in the Thai capital in what are becoming some of the largest demonstrations since the deadly street protests of 2010.

Up to 100,000 opponents of Prime Minister Yingluck Shinawatra gathered in sites across the city, calling for her resignation.

While across the city, between 40- and 50-thousand pro-government "red shirts" rallied in support of her administration.

Thailand has faced weeks of protests sparked by a blanket amnesty bill that would have allowed the prime minister's older brother, Thaksin Shinawatra, who lives overseas, to avoid a two-year jail term for corruption.

The bill would have also pardoned former prime minister and Democrat Party leader Abhisit Vejjajiva, who has been indicted for murder for ordering a crackdown on protesters in 2010.

Former deputy prime minister and opposition leader Suthep Thaugsuban has urged protesters to continue their demonstrations and called for civil servants to join in on them.

The opposition Democratic Party will also lead a a no-confidence debate in the lower house this week, despite being vastly outnumbered by Yingluck's Pheu Thai Party.