Thousands march against lacklustre education system while others protest with giant "asteroid" balls and half a dozen T-Rex characters representing the country's "political dinosaurs".
At least 41 people have been wounded after anti-government demonstrations turned violent, medics say.
Prayuth’s government holds the majority in parliament because his junta picked the entire upper house before an election last year that opponents say was designed to keep him in power.
Protests since July have increasingly called for reforms to the powerful monarchy, breaking a long-standing taboo against criticising the institution, as well for the removal of Prime Minister Prayuth Chan-ocha and a new constitution.
The measures had also given the police carte-blanche to arrest protesters and seize electronic materials believed to threaten national security.
Legal aid group Thai Lawyers for Human Rights says at least 51 people have been arrested since Tuesday in connection with the protests.
Protesters in Thailand make their presence felt in the capital Bangkok seeking reforms.
The standoff between anti-government demonstrators demanding constitutional reforms and royalist supporters of King has evoked fears of troubles similar to those that led to the 2014 coup.
Protesters gathered in Bangkok for the most ambitious rally so far in a pro-democracy campaign that has shaken up the government and Thailand's conservative establishment.
Thailand's Constitutional Court dissolved the Future Forward Party and imposed a 10-year ban on the party's executive members holding political office.
Demonstrations come after Thailand's election panel asked Constitutional Court to dissolve the opposition Future Forward Party, accusing it of infringing laws by accepting multimillion-dollar loans from its leader.
King Vajiralongkorn, 66, became constitutional monarch after the death of his revered father, King Bhumibol Adulyadej, in October 2016 after 70 years on the throne. The coronation follows a period of mourning.
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