BANGKOK (REUTERS) - Thailand's King Bhumibol Adulyadej left hospital on Monday (Jan 11) to visit his Bangkok palace, his first such outing since he was admitted last year.

His trip to the Chitralada Palace follows a Royal Household Bureau announcement on Sunday that the 88-year-old king was recovering from a blood infection and swollen lung.

King Bhumibol, the world's longest serving monarch, has been in hospital since May and has received treatment for multiple illnesses. Nervousness over his health and the succession has formed the backdrop to a decade of political crisis in Thailand, where the military took power in a coup in May 2014.

"His Majesty will go to the Chitralada Palace for a change of atmosphere and will return today," said a palace official, who declined to be identified.

The King, who came to the throne in 1946, is widely revered and his absence during an annual audience to mark his birthday on Dec 5 heightened anxiety over his health. But he made a rare public appearance on Dec 14.

He has been mostly confined to hospital since 2009, though has spent some time at a palace called Klai Kangwon, which translates as "far from worries", in the seaside town of Hua Hin south of Bangkok.

Hundreds of people lined the streets around the hospital as the King left in a van wearing a Hawaiian-style shirt, according to a Reuters reporter at the scene. Some shouted "Long live the King".

"This is the best opportunity in my life to see him," said 49-year-old Nuananong Sripai. "I'm worried about his sickness and hope he will get better soon."

Thailand has a strict lese-majeste law which makes it a crime to defame, insult or threaten the king, queen, heir to the throne or regent.

Under the military government, prosecutions of those accused of defaming the royals have increased dramatically and sentences have become harsher.

The palace issues notices on the King's health and keeps tight control over news about the royal family.