The rally was called by royalist group 'Pitak Siam' (Protect Thailand) led by retired general Boonlert Kaewprasit who accused the administration of corruption and not cracking down on those disrespecting the monarchy.
As thousands swarmed the Bangkok's Royal Plaza and tried to break down the barriers, police fired tear gas shells to quell the irate protesters leaving many injured, the BBC reported.
The police had to call for an additional re-inforcements to keep the situation from blowing out.
Earlier in the day, Kaewprasit called for the removal of the government.
"I promise that Pitak Siam will succeed in driving this government out," former Gen Boonlert Kaewprasit said in his address to the rally, the report said.
The protests also brought anti-Shinawatra forces together including "yellow shirt" members of People's Alliance for Democracy.
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The government has invoked the Internal Security Act in three districts of the capital giving police the powers to ban gatherings, block routes and, if need be, carry out searches.
The current protests brings tumultuous politics in Thailand to centrestage and also the role of ex-premier Thaksin Shinawatra, who many say controls the government through "remote control."
He was ousted in 2006 after a military coup and had fled the country in 2008 after being charged with abuse of power.