A pro-monarchy supporter rides on a motorway wearing a suit of armor in Bangkok, Thailand, on Thursday (September 24).

The supporter of King Maha Vajiralongkorn, or Rama X, rode a quad bike decorated with flags, weapons and portraits on the same day that hundreds of activists surrounded the parliament.

Democracy activists are demanding changes to the country's constitution which would limit the power of the royal family.

However, the rallies - which have been growing in recent months - have sparked a backlash from supporters of the revered institution, which is protected by strict lese majeste laws.

For many Thais, the monarchy provides a strong sense of order, cultural identity and connection to history.

The demonstration came on the same day that King Maha Vajiralongkorn arrived in Thailand for a brief visit from Europe to mark Prince Mahidol Day.

Officers prepared water cannon trucks to quell any violence or unrest during the daring protest. A democracy plaque was also sprayed in gold paint outside the Parliament House following the installation of a similar plaque at the weekend when thousands of protesters converged on the Sanum Luang royal field in front of the Grand Palace in Bangkok.

The rallies marked one of the most direct confrontations against the country's monarchy ever seen. Dozens of protests have been held in recent months amid anger from activists.

Opponents of the ruling military party, which seized power in a coup in 2014 and won elections in 2019, are critical of the army's strong-arm tactics to silence critics to maintain its grip on power. Wide-ranging complaints include a lack of transparency, low levels of democracy, economic equality and issues with the country's reputation for police and political country.