Senior Sikh leader Gurcharan Singh Tohra is in hospital in northern India after suffering a massive heart attack.
Mr Tohra is a veteran religious and political leader
Mr Tohra, 80, heads the Sikh Gurdwara Prabandhak Committee, the body charged with administering Sikh religious and cultural institutions worldwide.
A doctor in the Sikh holy city of Amritsar said his condition was "critical". The leader was taken to hospital after prayers on Thursday.
Mr Tohra is also a leader in the Sikh political party, Shiromani Akali Dal.
The Akali Dal has allied with India's governing Bharatiya Janata Party for nationwide elections due in April.
Uprising and Infighting
Mr Tohra, a veteran leader, has held the office of president of the Gurdwara Prabandhak Committee 26 times.
Sikh political parties and religious bodies are closely entwined in India's Punjab state, where Sikhs are in a majority.
The Akali Dal party offered political backing to a separatist struggle waged by Sikh guerrillas during the 1980s.
The party shifted ground in the early 199os, moving closer to New Delhi.
At the same time, Indian security forces gained the upper hand against the Sikh militants.
Mr Tohra survived an assassination attempt by suspected militants in 1990, which left his driver and an associate dead.
The Sikh uprising was effectively quelled by the mid-1990s, but a feud then erupted within the Akali Dal, as Mr Tohra quarrelled with Prakash Singh Badal, the then-chief minister of Punjab state.
The feud was eventually resolved.