Cambodia's ailing former king Norodom Sihanouk left his country for Beijing to undergo medical tests, officials said. The 88-year-old monarch, who remains a revered figure in Cambodia, was on Wednesday given a red-carpet sendoff by his son King Norodom Sihamoni, Prime Minister Hun Sen and other senior government officials at Phnom Penh airport. Sihanouk has suffered from a numbr of ailments, including cancer, diabetes and hypertension, and has received the bulk of his medical treatment in China, although he had been back in Phnom Penh since early April. "He goes back this time to have his health checked to stay healthy and live longer among his people," Prince Sisowath Sirirath, second deputy president of the royalist Funcinpec party, told reporters. He said he didn't know when Sihanouk would next return. Sihanouk, who was travelling with his wife, appeared cheerful and well rested as he pressed his hands together in a traditional greeting to well-wishers before boarding his plane. One of Asia's longest-serving monarchs, the former king abruptly quit the throne in October 2004 in favour of his son, citing old age and health problems. Despite abdicating, the ex-monarch sometimes uses his website to communicate with the outside world. In his most recent message, dated July 30, he apologised for being too tired to receive visitors. "The truth is that... I often fall asleep," he wrote in a handwritten letter posted online. "I spend most of my time in my bedroom." He said in 2009 he had lived too long and wished to die as soon as possible, according to another note on his website. "Lengthy longevity bears on me like an unbearable weight," he said.