BANGKOK — Thailand's 85-year-old king is set to leave the hospital where he has lived since being admitted for lung inflammation four years ago and return to his seaside palace, officials said Wednesday.

King Bhumibol Adulyadej and Queen Sirikit were scheduled to travel Thursday to Klai Kangwon Palace in the town of Hua Hin, where they were living before the world's longest-reigning monarch was hospitalized in September 2009.

The Royal Household Bureau said the king and queen would leave Siriraj Hospital and travel by car to the seaside royal residence, according to Prachuap Khiri Khan provincial governor Veera Sriwattanatrakul.

Veera said the palace did not say whether the move would be permanent.

Hua Hin, a seaside town in the southern province of Prachuap Khiri Khan, is about a 2 1/2 -hour drive south of Bangkok.

"We have checked the road conditions, cleaned up the streets and put up the national and the royal flags along the way to the palace," Veera said by telephone. "The province will also prepare 11 parking spots for well-wishers who want to greet Their Majesties."

Veera said about 10,000 people were expected to welcome the king and queen in Hua Hin.

Bhumibol actively worked for decades on behalf of Thailand's poor, but has almost disappeared from public life since he was hospitalized for what the palace called a lung inflammation.

Since then, he has had a variety of ailments and has lived in a royal wing of Siriraj Hospital, leaving only on rare occasions and always in a wheelchair.

The 80-year-old queen was admitted to the same hospital in July last year when she experienced dizziness and staggered slightly while walking for exercise.

Bhumibol is a widely revered figure in Thailand, and news of the royal family's health is carefully watched.