The Deputy Prime Minister confirmed the appointment of Prem Tinsulanonda as candlelight vigils were held across the country.
Inside Thailand's Grand Palace is where the resting place of the body of the world's longest reigning monarch will stay until a royal funeral takes place.
Last night monks gathered to pray with members of the Royal family as one year of official mourning begins.
The heir to the throne, Crown Prince Maha Vajiralongkorn performed funeral rituals as he takes time to grieve.
The Thai government has confirmed retired military officer and former Prime Minister Prem Tinsulanonda will be temporary regent. However, has stressed that Prince Vajiralongkorn will still take the throne.
Water ceremonies will take place every night for at least the next 100 days as the King's body is prepared to be cremated.
For seventy years King Bhumibol was head of state, most people only ever knowing one King. Mourner Jantanee Taumtub said he was an anchor of stability through decades of upheaval.
"Every time I feel I'm not okay and having problems, I'll think of his teachings. His words that he gave us are very precious and whoever followed it will lead to happy life," said Ms Taumtub.
No matter what time of day, people are flocking to the Palace to pay their respects. Some even sleeping overnight.
Mourner Kraivut Khajohnpob said he just wants to be close to his King for as long as possible.
Thailand's King Bhumibol Adulyadej. (AAP) Source: EPA
"He is not only the father to us, but way more beyond that," said Mr Khajohnpob.
Right across Thailand the sorrow is palpable. In the south Muslims have gathered to pray and pay their respects. Muslim community leader Surin Parare says they are mourning despite differences in religion.
"I would like to urge people to be united as Muslims and Buddhists are brothers. Don't be divided. I love the King as any other person," said Mr Parare.
Earlier in the day thousands wearing black lined city streets between the hospital and the Grand Palace to see the hearse pass by.
Many waited for hours in stifling heat to catch a glimpse of their beloved monarch before he was taken inside the Palace.
