Thousands of Thais have been holding late-night vigils at Bangkok's royal palace to mourn King Bhumibol Adulyadej, who died on Thursday.
Having been on the throne for 70 years, King Bhumibol was the world's longest-reigning monarch.
His body was brought to the palace in a convoy flanked by saluting soldiers and massive crowds of mourners who lined the streets, weeping. Millions of people watched live on TV.
Crown Prince Maha Vajiralongkorn has been named as successor, but has asked for a delay in the process.
A 96-year-old former prime minister of Thailand, Prem Tinsulanonda, who is head of the Privy Council, which advises the sovereign, has meanwhile been appointed as regent.
Thailand has entered an official year of mourning after King Bhumibol died on Thursday, aged 88. The cabinet declared Friday a government holiday, and flags will fly at half-mast for the next 30 days.
People have been asked to wear black and avoid "joyful events" during this time. Film screenings, concerts and sports events have been cancelled or postponed.
News websites turned their pages black and white. All television channels in Thailand aired state media programmes, including live coverage of the day's events.
Black-and-white footage of the king's life, including him playing the saxophone, replaced regular transmissions on television channels shortly after his death was announced.
Most people in the capital and in towns across the country dressed in black, but shops opened for business.
Body carried to Buddhist temple
The crown prince travelled in the convoy carrying the king's body to the Temple of the Emerald Buddha in the Royal Palace.
Most Thais have known no other monarch and King Bhumibol's picture is hung in almost every house, school and office.
AFP news agency quoted 77-year-old mourner Phongsri Chompoonuch as saying "we no longer have him".
"I don't know whether I can accept that. I fear, because I don't know what will come next."
Suthad Kongyeam, 53, who was at the Grand Palace waiting for the convoy to arrive, said it felt like losing a father.
"He was the heart of the whole country," he said. "Everything is shaken. There is nothing to hold on to anymore."
After the convoy arrived at the temple, the crown prince bathed the king's body, a traditional Thai Buddhist funeral rite.
Buddhist monks then said prayers over the king's remains. His body will be on display for people to pay their respects.
It could be months before the late king's cremation.
King a unifying force
King Bhumibol earned the devotion of the Thai people for his efforts to help the rural poor, including agricultural development projects and charity works.
Until his later years, he was featured on television almost every evening, often trudging through rain, map in hand and camera around his neck, visiting a rural development project.
His wife, Queen Sirikit, 84, has also been in poor health in recent years.
The monarch was also seen as a stabilising figure in a country often wracked by political turmoil.
The military, which took power in a 2014 coup, has for decades invoked its duty to defend the monarchy to justify its intervention in politics.
The country has suffered a decade of turmoil including two coups and deadly protests in the capital, as well as a long-running Muslim separatist insurgency in the south, with regular small-scale bomb attacks.
Though the constitutional monarch has limited official powers, many in the nation of 67 million people looked to King Bhumibol to intervene in times of high tension. He was seen as a calming influence through numerous coups and 20 constitutions.
However, his critics argued he had endorsed military takeovers and at times had failed to speak out against human rights abuses.
Prime Minister Prayuth Chan-ocha has said security is his top priority and he ordered extra troops deployed around the country.
The junta has promised an election next year and pushed through a constitution to ensure its oversight of civilian governments. It looks firmly in control for a royal transition.
The Prime Minister warned against anyone taking advantage of the situation to cause trouble.
The crown prince, 64, is much less well known to the Thai people and he has not attained his father's widespread popularity. He has married and divorced three times and spends much of his time overseas, often in Germany.
Prime Minister Prayuth Chan-ocha said the crown prince had asked for a delay in the succession as he wanted time to mourn with the nation.
Privy Council President Prem Tinsulanonda will act as regent until the Thai assembly invites the heir to succeed to the throne, the military government confirmed.
Strict lese-majeste laws protect the most senior members of Thailand's royal family from insult or threat. Public discussion of the succession can be punishable by lengthy jail terms.
Given the pivotal role the king has played in maintaining the balance of power, the succession will be a formidable challenge for the government, the BBC's Jonathan Head said.
- BBC, Reuters