Thailand's Crown Prince Vajiralongkorn wants to delay being proclaimed king so that he can mourn the death of his father, Prime Minister Prayut Chan-o-cha said, local media reported.
"He requested time to deal with his grief and express his sadness alongside the people across the nation at this time," Prayut said, according to Khaosod news service.
"As for the succession, he wishes to wait until the appropriate time."
King Bhumibol Adulyadej, the world's longest-reigning monarch, died peacefully Thursday at a Bangkok hospital, the royal household bureau said. The 88-year-old's last public appearance had been in January.
Bhumibol was a beloved and deeply revered figure in Thailand whose seven decades on the throne provided a constant backdrop of stability to the frequent turbulence of the country's politics.
Hundreds of his supporters gathered outside the hospital, many of them in tears. Several held up images of Bhumibol and offered prayers, while others joined in Buddhist chants.
The crowd also stood and sang the king's anthem. Many were dressed in yellow shirts, the king's colour, and pink ones, designated for prayer sessions earlier in the day. But by nightfall, the majority of mourners came dressed in black.
One man, Theppachart Khongkoet, who was dressed in black and holding a yellow garland, said he had planned to visit the hospital on Friday to pay his respects. "But it is all too late now," he said, sobbing uncontrollably.
Another woman spoke of the way Bhumibol impacted her life.
"This will not change my life because my life has already been changed," said Wimonmarn Sawasdee, 51, a business owner.
"I used to work for status and money but not anymore. His majesty taught me to live sufficiently and to think about other people and not just myself," she added.
Many soldiers and police officers were also at the scene, trying to usher people off the hospital grounds.
Exhalted by Thais as semi-divine, Bhumibol enjoyed near-universal admiration, serving as a unifying figure in the country throughout his reign. He ascended to the throne on June 9, 1946.
Following the king's death, Thailand was set to enter a one-year mourning period, Prayut said in a nationally televised address.
"Even though we are in mourning, our beloved country needs to move forward. Do not let this death hold us back from following through with his majesty's vision of prosperity and peace," Prayut added.
Prayut called the king's death the "country's biggest loss" since 1946, when King Rama VIII, Bhumibol's brother, died unexpectedly.
The premier urged the public to refrain from rash stock market decisions, telling Thais to uphold the country's financial credibility by refraining from short selling and panic buying.
Vajiralongkorn, 64, and other royal family members were present when the king died, according to the Bangkok Post, whose website featured only black and white colours after the news.
Public buildings were asked to lower their flags for 30 days beginning Friday, and the public was urged not to hold any form of celebration for 30 days.
Public sector employees were asked to wear black for one year. The general public was also encouraged to wear black during that time, but the suggestion was not mandatory, the premier said.
After the announcement of the king's death, local television channels began broadcasting scenes from Bhumibol's life, highlighting his devotion to rural communities and ordinary Thai citizens.
World leaders swiftly issued their condolences to Thailand and to the Thai royal family.
"His Majesty was a tireless champion of his country's development and demonstrated unflagging devotion to improving the standard of living of the Thai people," said US President Barack Obama, who met the king in 2012.
United Nations Secretary-General Ban Ki-moon also expressed his sympathy while praising Bhumibol for his "long dedication to his country and his legacy as a unifying national leader."
Bhumibol received a Lifetime Achievement Award from the United Nations Development Programme in 2006.