BANGKOK — Thousands of Thai protesters called on King Maha Vajiralongkorn on Wednesday (Nov 25) to cede control of a royal fortune valued in the tens of billions of dollars, the latest in months of demonstrations focused squarely on the monarchy.

The protesters have broken a longstanding taboo by criticising the king, and police summoned many of the best-known protest leaders on Tuesday on charges of insulting the monarchy, which can mean up to 15 years in prison.

Protesters demonstrated outside the headquarters of the Siam Commercial Bank, Thailand's biggest bank, in which the king's 23 per cent stake worth over US$2.3 billion (S$3.09 billion) makes him the largest shareholder.

"The people demand back national assets from the king," read one protest banner.

Police put the number of protesters at 8,000.

Mr Parit Chiwarak, among those facing royal insult charges, said: "Millions of families are struggling so how can we give our taxpayers' money to just one family to spend luxuriously?"

The total value of the royal holdings is not made public, but is estimated to be worth more than US$30 billion.

Wednesday's protest was moved to the SCB headquarters after police built siege barricades of shipping containers and razor wire around the Crown Property Bureau, which manages the royal assets and where the rally had originally been planned.

"The SCB shares should not belong to the king but the finance ministry, so the dividend can be used to develop the country," said Mr Boss, 28, one of the protesters.

The shares rose more than two per cent, in line with other banks.

The palace has made no comment since the protests began, but when the king was asked about the protesters recently he said they were loved "all the same".

Some of the king's critics quoted those words sarcastically after the summonses on charges of insulting the monarchy, which prime minister Prayuth Chan-ocha had said in June were not being used at the request of the king.

International human rights groups condemned the use of the charges. Police sources said 15 protest leaders faced the charges, which they must acknowledge by the end of the month.

Responding to the criticism, government spokeswoman Rachada Dhnadirek defended the use of the charges.

Since July, protesters have been calling for the removal of Mr Prayuth, a former junta leader. They accuse him of engineering last year's election to keep hold of power he seized in a 2014 coup. He says the ballot was fair.

The protesters seek to make the king more accountable under the constitution as well as the reversal of changes which gave him personal control of some army units and the royal fortune.

Wearing yellow shirts, in the king's colour, hundreds of well-wishers gathered to greet him ahead of an event in Bangkok.

"We're here to protect the king. The king is the key to the unity of the people," said Ms Santi Yanothai, 67. REUTERS