Manmohan Singh, the former Indian prime minister whose economic reforms made his country a global powerhouse, has died at the age of 92, current leader Narendra Modi said on Thursday.

India "mourns the loss of one of its most distinguished leaders," Modi posted on social media platform X shortly after news broke of Singh's passing.

"As our Prime Minister, he made extensive efforts to improve people's lives."

Singh was taken to a hospital in New Delhi after he lost consciousness at his home on Thursday, but could not be resuscitated and was pronounced dead at 9:51 pm local time, according to a statement by the All India Institute of Medical Sciences.

Singh, who held office from 2004 to 2014, is credited with having overseen an economic boom in Asia's fourth-largest economy in his first term, although slowing growth in later years marred his second stint.

"I have lost a mentor and guide," opposition Congress leader Rahul Gandhi said in a statement, adding that Singh had "led India with immense wisdom and integrity."

"Millions of us who admired him will remember him with the utmost pride," said Gandhi, a scion of India's powerful Nehru-Gandhi dynasty and the most prominent challenger to Modi.

Mallikarjun Kharge, leader of the opposition in parliament's upper house, said "India has lost a visionary statesman, a leader of unimpeachable integrity, and an economist of unparalleled stature."

President Droupadi Murmu wrote on X that Singh will "always be remembered for his service to the nation, his unblemished political life and his utmost humility."

Born in 1932 in the mud-house village of Gah in what is now Pakistan, Singh studied economics to find a way to eradicate poverty in India and never held elected office before taking the vast nation's top job.

He won scholarships to attend both Cambridge, where he obtained a first in economics, and Oxford, where he completed his PhD.

Singh worked in a string of senior civil posts, served as a central bank governor and also held various jobs with global agencies including the United Nations.

He was tapped in 1991 by then Congress prime minister P.V. Narasimha Rao to reel India back from the worst financial crisis in its modern history.

In his first term Singh steered the economy through a period of nine-percent growth, lending India the international clout it had long sought. (AFP)