BANGKOK - Tens of thousands of anti-government demonstrators massed in Bangkok on Sunday, with a major rally scheduled later by their rivals, as Thailand faces its most significant political street action since bloody protests in 2010.
Organisers said 100,000 anti-government protesters had gathered by Sunday afternoon, while thousands of pro-government "Red Shirts" were expected to mobilise later at a suburban football stadium in support of Prime Minister Yingluck Shinawatra's crisis-hit administration.
Both groups have vowed to remain in the capital overnight as tension rises in a city which has seen several bouts of unrest since Prime Minister Thaksin Shinawatra - Yingluck's brother - was deposed in a military coup seven years ago.
Authorities said they expect opposition protesters to try to march on parliament and Government House on Monday, but vowed to show restraint.
"We will not use force and we will try to avoid any casualties," police spokesman Piya Utayo told AFP, estimating the anti-government rally to be at least 30,000-strong.
The Thai capital has already faced weeks of opposition-backed rallies sparked by an amnesty bill that could have allowed the return of Thaksin from self-imposed exile - and pardoned those responsible for a deadly military crackdown on his Red Shirt supporters.
The bill was rejected by the senate, but anti-government protesters have remained on the streets and are now trying to topple the government, which they say acts as a stooge for Thaksin.
Aerial footage showed tens of thousands of protesters crammed into the streets leading to the city's Democracy Monument, which has become the focus of the anti-government protests.
Addressing the rally, protest leader Satit Wongnongtaey hailed the strong turnout for the so-called "People's Day" rally, with many demonstrators arriving from the provinces.
"How can this government survive? How can the Thaksin system survive?" he said to applause from the crowd.