SINGAPORE - Former president S R Nathan is in critical condition after suffering a stroke on Sunday (July 31) morning, said the Prime Minister's Office (PMO) in a statement.
The 92-year-old is warded in the Intensive Care Unit at the Singapore General Hospital (SGH), the statement added.
Mr Nathan is Singapore's sixth and longest-serving president, having served two six-year terms as head of state from 1999 to 2011.
He has also served Singapore as a social worker, trade union activist, and diplomat in a public service career that spanned five decades.
In 2013, he became the seventh person in Singapore's history to be conferred the top National Day honour - the Order of Temasek (First Class) - for his exemplary service to the nation.
Mr Nathan's successor, Dr Tony Tan Keng Yam, said in a Facebook post that he and his wife Mary Tan were sad to hear about Mr Nathan's hospitalisation.
"Our thoughts and prayers are with his wife and family," he wrote.
Dr Tan and his wife arrived at SGH on Sunday afternoon to visit Mr Nathan.
He said in a subsequent Facebook post that he saw Mr Nathan and spoke with his family.
Prime Minister Lee Hsien Loong, who was on his way to Washington for an official visit to the United States, said he was saddened to learn about Mr Nathan's stroke and his grave condition. He added that he has been in touch with Mr Nathan's family.
"Mr Nathan served as our Ambassador to the US in the 1990s, among many contributions in a long career. He made many good friends for Singapore, and planted many seeds, including this beautiful antique Littleleaf Japanese Maple at our Washington DC embassy," he wrote in a Facebook post which was accompanied by a picture of the tree. "We have him in our thoughts and prayers."
Ministers past and present, as well as close friends of Mr Nathan, also visited him at the hospital.
Deputy Prime Minister Teo Chee Hean was seen arriving at SGH at around 3.20pm. Mr Teo is acting Prime Minister during Mr Lee's absence.
"Our thoughts and prayers, including those of PM Lee and Mrs Lee who are currently in the US, are with Mr Nathan, Mrs Nathan and the family," Mr Teo later wrote in a Facebook post.
Emeritus Senior Minister Goh Chok Tong said Mr Nathan's vital signs were stable, according to the doctor who was there when he visited the former president in the evening.
Mr Goh, who last met Mr Nathan three to four months ago at the former president's home in Joo Chiat, said: "He is a fighter. He has gone through this many times."
Defence Minister Ng Eng Hen revealed on Facebook that Mr Nathan had penned a letter to him just last week, where he shared how he had a stroke a year ago and recovered.
"He then added pensively that he had 'soldiered on and hoped to stay active for another year, before I call it a day'," Dr Ng wrote.
"What a remarkable man, I thought to myself. It could not be easy, but even at this age and with declining health, Mr Nathan still wanted to contribute and make a difference in the lives of others, at least for another year."
Foreign Affairs Minister Vivian Balakrishnan, who was accompanying PM Lee on the US visit, said he heard the news about Mr Nathan's illness while he was on his way to Washington. He wrote in a Facebook post: "Praying for his recovery. Poignant memories of his time in Washington as our ambassador to the USA."
Minister in the Prime Minister's Office Chan Chun Sing, who is also in PM Lee's delegation, said: "Saddened to hear that former president S R Nathan is currently in intensive care after suffering a stroke. My thoughts are with his family during this trying period. Let's keep him in our prayers and for him to have a speedy recovery."
Former Speaker of Parliament Abdullah Tarmugi and former Senior Minister of State Zainul Abidin Rasheed were also among those who visited Mr Nathan.
Speaking to reporters after his visit, Mr Zainul said he was shocked to hear the news because he met Mr Nathan just last week and he was in "top spirits". He revealed that Mr Nathan is still unconscious and not sedated.
"He (Mr Nathan) was really in top spirits and talking about the contributions of the Malay-Muslim communit," he added, referring to the book Majulah! 50 Years Of Malay/Muslim Community In Singapore that Mr Nathan helped launch on May 29.
The book launch was one of Mr Nathan's more recent public appearances.
Mr Abdullah added: "I think all Singaporeans are quite shocked and concerned. We knew that he had been ill for some time and were so shocked that he had a stroke...naturally his family is concerned."
Former Cabinet minister S Dhanabalan told reporters at the hospital that he last spoke to Mr Nathan on the phone two weeks ago.
In a Facebook post, former deputy prime minister Wong Kan Seng said he visited Mr Nathan at his home 10 days ago and that he was alert and in good spirits.
Last April, Mr Nathan suffered a stroke and was warded at SGH for almost three weeks before he was discharged.
Mr Nathan and his wife, former teacher Urmila Nandey, have two children - a son and a daughter - and three grandchildren.
Starting out as a medical social worker and then a seaman's welfare officer in 1955, Mr Nathan was made an assistant director of the National Trade Union Congress' Labour Research Unit in 1961, where he worked with the late deputy prime minister Goh Keng Swee.
He then joined the Ministry of Foreign Affairs' political divison, and led a team of Singapore officials during the 1974 Laju incident when a ferry was hijacked by terrorists.
He subsequently took on the role of executive chairman at the newly formed Straits Times Press from 1982 to 1988, before serving diplomatic stints as the High Commissioner to Kuala Lumpur (1988-1990) and Singapore's Ambassador to the United States (1990-1996).