Thai King Bhumibol Adulyadej, the wolrd's longest reigning monarch, urged the Thai people to stay unified and strengthen friendship, as the country celebrates his 85th birthday on Wednesday.

The monarch thanked his subjects for their birthday blessings in a public audience Wednesday morning at the open balcony of the Ananta Samakhom Throne Hall near the Royal Plaza.

"I am gratified to see the well-wish, 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.

The ceremony was attended by members of royal families, including the Crown Prince Maha Vajiralongkorn and Princess Maha Chakri Sirindhorn, the commanders of the three branches of the Armed Forces, legislators and diplomats. Prime Minister Yingluck Shinawatra, House Speaker Somsak Kiatsuranont, Supreme Court President Phairoj Wayuparp and Supreme Commander Thanasak Patimaprakorn gave congratulatory speeches to pay homage to the King.

Around 200,000 people, lined the streets from Siriraj hospital, where the King has been staying for more than three years, to the Royal Plaza to join the birthday celebration.

Many of the yellow-clad and flag-waving well-wishers camped out in front of the hall since Tuesday evening, hoping to catch a glimpse of the King. Some of them shed tears as they kept chanting "long live the king."

In Thai culture, yellow is the color representing Monday, the day of the King's birth.

Queen Sirikit did not accompany the king for the grand audience at the hall on the advice of her doctors, according to a statement issued earlier by the Royal Household Bureau.

Last year, the monarch appeared on the main balcony at 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 disaster in its history.

King Bhumibol came to the throne in 1946 and is now the longest reigning monarch in the world, widely revered across the kingdom. He was admitted to hospital in September 2009 for pneumonia and has since stayed there and rarely made public appearance.