The last time the royal couple greeted a crowd there was in 1999 on HM the King's 72nd birthday when he also gave a short speech to tens of thousands.

The King told his subjects to review themselves and contribute to the nation with compassion that would lead to unity and prosperity.

To view Friday's event, people are advised to arrive before 7am and take traffic disruption into account.

At about 10am, the King and Queen will take part in a religious ceremony to pay homage to previous kings.

The chief Brahmin priest will conduct the ceremony and afterwards a court astrologer will strike a gong.

Another priest will blow a large conch shell and an orchestra is due to perform as the royal couple offer basic necessities to senior monks.

Later, Their Majesties will meet the Royal Family and other descendants of the Chakri Dynasty in the throne hall and the Privy Council.

His Royal Highness Crown Prince Maha Vajiralongkorn

will offer blessings to the King with flowers, candles and joss sticks on behalf of the Royal Family.

The prime minister and the presidents of the Senate and Supreme Court, Cabinet members, diplomats, parliamentarians, senior civil servants and judges will also be present.