Thai police Thursday arrested several more prominent activists involved in the kingdom's young pro-democracy movement, which is demanding an overhaul of the government and breaking taboos by calling for reforms to the monarchy.

Thailand has seen near-daily rallies for over a month with some 20,000 turning out at the weekend to vent their anger at the military-aligned government and call for discussions about the royal family's role.

Overnight, police detained three key activists before taking five more into custody Thursday morning, including two outspoken rap stars -- taking the total to 11 arrests. 

Four further arrest warrants had been issued, police told reporters Thursday. Those detained had "all joined the protest on 18 July," said Karoon Hosakul, an MP from the opposition Pheu Thai party, referring to a demonstration in Bangkok that kicked off the wave of rallies.

They all face eight charges, including sedition, he confirmed. Dechatorn Bamrungmuang from Rap Against Dictatorship (RAD) and Thanayut Na Ayutthaya, better known as rapper "Elevenfinger", both performed on stage at the event.

RAD's track "What My Country's Got?" -- an indictment of military oppression -- has racked up more than 87 million views since its release ahead of last year's election.

The poll saw ex-army chief and mastermind of the 2014 coup Prayut Chan-O-Cha sweep to power.

But protesters say the vote was stacked in his favour thanks to a constitution scripted by the military in 2017. 

They are demanding parliament be dissolved and the constitution rewritten.

Thursday's detentions came after the re-arrest late Wednesday of human rights lawyer Anon Numpa for his participation at another protest on August 3.

He was one of the first activists to openly discuss reforming the monarchy at the Harry Potter-themed event.

The movement is calling for greater transparency of palace finances and for a controversial royal defamation law -- which carries jail sentences of up to 15 years -- to be scrapped.

King Maha Vajiralongkorn is hugely powerful, supported by the arch-royalist military and the country's billionaire clans.

Since he ascended the throne in 2016, he has made unprecedented changes to the institution -- including amassing direct control of the palace's fortune, which is estimated to be worth up to $60 billion. 

Many of Thailand's high school students have taken up the pro-democracy fight, tying white bows in their hair and on backpacks in solidarity with the cause.

So far no activists have been charged under the lese-majeste law, but their perceived affront to the monarchy has triggered several smaller counter-demonstrations by royalists.