One of India's most revered spiritual leaders, Satya Sai Baba, is in a critical condition, doctors say.
Thousands of devotees in the state of Andhra Pradesh have gathered outside a hospital where he was admitted last week with breathing problems.
State security forces have increased their presence around the hospital in Puttaparthi as devotees prayed for his wellbeing there.
The 85-year-old guru is thought to have millions of followers around the world.
His distinctive orange robes and his hair have made him one of the most recognisable of India's spiritual gurus.
He professes to be the reincarnation of a Hindu godman --a human being who declares himself divine - from the 19th Century.
Sai Baba counts former Indian prime ministers, prominent businessmen and India's cricketers among his followers.
He commands huge audiences at the local ashram (religious retreat), where devotees say he performs countless "miracles".
But his career has also been dogged by controversy. He has been accused of faking some of the "miracles" attributed to him.
And some former followers levelled accusations of sexual abuse against him and other members of his ashram - a charge that he has denied.
He has never been charged by police in connection with these allegations.
Sai Baba was admitted to a hospital in Puttaparthi, where he is based, last week with lung and chest congestion, doctors say.
A health bulletin issued by the hospital said that his condition had deteriorated and he is now on a ventilator and receiving kidney dialysis.
"The vital systems are not adequately responding. The condition of Baba is critical. The panel of doctors treating him are doing their best to make the systems respond," hospital director AN Safaya said in a statement.