Thai King Bhumibol Adulyadej, the world's longest reigning monarch, urged Wednesday his subjects to stay unified and strengthen friendship as people across the country celebrate his 85th birthday.

The monarch granted a rare public audience Wednesday morning at the open balcony of the Ananta Samakhom Throne Hall near the Royal Plaza, where around 200,000 people have gathered since Tuesday night to join the celebration.

He thanked his people for their birthday blessings. "I am gratified to see the well-wishes, friendship and unity you all have shown today. I believe that it will make our country even more unified," he said.

"If the Thais could maintain this kind of friendship and unity, I strongly believe that our country can stay stable, secure and happy, no matter under what circumstances." he added.

Last year, the monarch appeared on the main balcony of the Chakri Maha Prasat Throne Hall at the Grand Palace to mark his 84th birthday, calling for national unity and stability as the country just went through one of the greatest flood disasters in its history.