The equestrian statue of the late monarch, also known as King Rama V, can be seen in the middle of the plaza.
Prayut and his entourage also placed floral wreaths in front of the statue to show their deep respect to the king, who in 1905 peacefully abolished slavery in Thailand.
The prime minister was also to preside over a candlelight ceremony at the Sanam Luang grounds to honour King Rama V.