Thai King Bhumibol Adulyadej lights a candle on Monday as he marked the 64th anniversary of his coronation at the Klai Kanwon Palace. Photo: AFP

Thailand's revered King Bhumibol Adulyadej made a rare public appearance Monday to mark the 64th anniversary of his coronation, as the political turmoil gripping his kingdom enters a critical phase.

Embattled Prime Minister Yingluck Shinawatra is facing two key legal challenges which could see her removed from office over the coming days, while opposition leader Abhisit Vejjajiva refused at the weekend to commit to elections mooted for July to end the political crisis.

King Bhumibol, the world's longest-reigning monarch and a father figure for Thais, was crowned on May 5, 1950, although he came to the throne in June 1946 following the death of his elder brother.

The 86-year-old monarch is seen as a moral authority in Thailand, which has been deeply divided along political lines since 2006 when billionaire former premier Thaksin Shinawatra - Yingluck's older brother - was ousted in a military coup.

King Bhumibol's public speeches are closely scrutinized, especially in times of political crisis, but on this occasion he did not speak.

The streets of Hua Hin, near the coastal palace where the monarch has lived since leaving a Bangkok hospital in August, were a sea of yellow - his signature color - as his vehicle passed, with thousands of people waving flags and shouting "long live the king."

A short service was held in a room in the royal palace packed with Thailand's political and military establishment, as well as senior members of the royal family, including the heir Crown Prince Maha Vajiralongkorn.

Monks led prayers as the king, who has suffered ill health for several years and uses a wheelchair, looked on.

Yingluck was also present. She has faced six months of protests demanding she steps down.

AFP