Zsa Zsa Gabor was rushed to hospital on Monday - just two days after her 99th birthday.
The US actress was taken to the medical facility in Los Angeles due to breathing difficulties, two days after she turned 99, her husband Frederic von Anhalt has revealed.
According to TMZ, Zsa Zsa - who hasn't been seen in public for years - was diagnosed with a feeding tube-related lung infection.
The 99-year-old star is to have surgery to get her breathing tube removed.
Doctors are said to have initially tried to cure the 'Moulin Rouge' actress at her home by attempting to remove mucus from her throat.
Zsa Zsa has suffered with health problems since 2002 when she was a front seat passenger in a car crash in Sunset Boulevard, Los Angeles, which left her partially paralysed and confined to a wheelchair.
She later suffered a stroke in 2005 and again in 2007, and in 2010 she had hip replacement surgery after fracturing the joint.
The actress had to have her right leg amputated in life-saving surgery in 2011 after it became infected with gangrene.
Zsa Zsa has outlived her only daughter, Francesca Gabor Hilton, who died aged 67 in January 2015 after she suffered a huge stroke.
Francesca - whose father was the late Hilton Hotel founder Conrad Hilton - worked as a professional photographer, comedienne and a publicist for the stars and once dated late comedy actor Peter Sellers, who died in 1980.