The coronation represents a renewal of the monarchy's power after the October 2016 death at age 88 of Vajiralongkorn's revered father, King Bhumibol Adulyadej. It also comes amid more than a decade of political strife, including a 2014 military coup and a contentious election less than two months ago.
After completing the rites on Saturday, Vajiralongkorn issued his post-coronation royal command, which is supposed to set the tone for his reign. It closely echoed the words of his father's first command.
"I shall continue, preserve, and build upon the royal legacy and shall reign with righteousness for the benefit and happiness of the people forever," the king said, according to an unofficial translation.
The 66-year-old Vajiralongkorn has served as king for more than two years since assuming the throne. On Saturday, he received his crown from the chief Brahmin, a Hindu priest who played a guiding role in the mixed Buddhist-Hindu ceremony, which was televised live across the nation on all channels.
The king, known as Rama X for being the 10th monarch in the Chakri dynasty, then placed the crown atop his head. The "Great Crown of Victory," said to date from 1782, is 66 centimeters (26 inches) high, weighs 7.3 kilograms (16 pounds) and is ornamented with diamonds set in gold enamel. It was one of several pieces of royal regalia, including the Royal Sword of Victory and the Royal Fan and Fly Whisk, presented in homage to his power.
Absolute rule by kings ended with a 1932 revolution in Thailand that ushered in a constitutional monarchy. Nevertheless, Thai kings are regarded as almost divine and have been seen as a unifying presence in a country that has seen regular bouts of political instability as it rotates between elected governments and military rule.
Vajiralongkorn since taking the throne has tightened control over royal institutions and acted to increase his influence in his country's administration. The powers he acquired centralize royal authority in his hands and make explicit his right to intervene in government affairs, especially in times of political crisis.
Like kings before him, Vajiralongkorn is protected by one of the world's strictest lese majeste laws, which makes criticism of him and other top royals punishable by up to 15 years in prison and has dampened open debate about the monarchy's role in society.
Vajiralongkorn began Saturday's coronation proceedings wearing a simple white robe as he entered a small pavilion where he was briefly showered with water from several holy rivers and ponds and other sources. Other water was poured on him from old royal water vessels. The rite, known as the Royal Purification Ceremony, took place amid music from drums, conch shells and other instruments. Outside the palace, artillery was fired in a salute to the monarch.
A second rite, the Royal Anointment Ceremony, completed the consecration portion of his coronation, giving him the legitimacy of being a fully sovereign king. Vajiralongkorn — having changed into gold-embroidered royal vestments — was seated on an octagonal throne, with the sides representing the cardinal points of the compass, and a dignitary seated at each point. Each poured holy water over the king's hand, along with a ninth representing the heavens.
That rite ended with the monarch being presented with a nine-tiered white umbrella of state, symbolizing his full consecration. "This ceremony is significant to Thailand because the monarchy ... is a very important institution of our country and is the soul of our nation," said Naowarat Buakluan, a civil servant. "If you ask why the ceremony is being held this year when his majesty has already ascended the throne, it's because this is the right moment. Previously we Thais were mourning the loss of our beloved late king."
Vajiralongkorn inherits a nation in political turmoil, with the powerful army entrenched in government for five years after staging a coup in 2014. An election held in March has been widely seen as rigged through convoluted election laws to favor the military and its preferred candidate, Prayuth Chan-ocha, who led the coup and has headed the government since then.
Vajiralongkorn, said prominent intellectual and social critic Sulak Sivaraksa, "doesn't like ceremony himself, personally, but when it is performed he wants it to be proper." When his father was cremated in 2017, Vajiralongkorn "insisted that everything had to be done properly."
"Likewise the coronation has to be done properly and he doesn't mind the expense, but it has to be done properly," Sulak said. Vajiralongkorn presented his wife with the traditional regalia of a Thai queen as one of his first acts after being crowned. On Wednesday he appointed Suthida Vajiralongkorn Na Ayudhya to be the country's queen. His father Bhumibol married his bride, Sirikit Kitiyakara, just a week before his own coronation, at which he named her his queen. Now 86 but ailing, she survives him.
After the 2 ½ hours of ceremonies ended, Vajiralongkorn stepped from his throne, walked in front of other royal family members and scattered in his path tiny flowers of silver and gold, representing heavenly gifts for them to collect.
Despite not being able to see the king in person, civil servants in uniform and members of the public wearing garb in the royal color of yellow gathered outside the Grand Palace to pay their respects.
"I feel glad and hopeful that the king ascends the throne after his father, King Rama IX, to be a guardian and the hope of the Thai people," said onlooker Amornrat Wangpan from Uttaradit province, 433 kilometers (269 miles) north of Bangkok. "It will be a civilized era having many things. I feel that Thailand is now opened to the light and now civilized."
Later Saturday, the king held an audience for members of the royal family, the Privy Council and the Cabinet, among other senior officials, where they vowed their allegiance to king and country, and he promised to work with them for the nation's benefit.
Some carefully vetted members of the public admitted to the palace grounds got a thrill later when Vajiralongkorn was carried on an ornately decorated palanquin to the Temple of the Emerald Buddha — usually considered Thai Buddhism's holiest site site — by a specially trained contingent of soldiers dressed in colorful ceremonial uniforms who marched in strict precision. The king, like his predecessors, made the short journey to vow to defend the Buddhist faith, the religion of more than 90% of Thailand's people.
On Sunday, there will be a 7-kilometer (4.3-mile) royal procession involving 343 men, in which the king will again be carried on his palanquin through nearby city streets to visit four important temples and allow the public to pay homage to him.
Monday will see the king greet the public from the balcony of the Grand Palace in the late afternoon and then hold a reception for the diplomatic corps.
Associated Press video journalist Tassanee Vejpongsa contributed to this report.