India's Prime Minister Manmohan Singh underwent successful coronary bypass surgery yesterday, while confusion emerged about who was in charge of government just months before a general election.

"The entire country is rejoiced because our Prime Minister, Dr Manmohan Singh, has come out, you know, successfully with the operation," ruling Congress party general secretary Veerappa Moily told reporters.

The 76-year-old leader may be unable to return to work for several weeks, just as his Congress party prepares its re-election campaign for a general election by May.

Doctors at the hospital were due to give a briefing on Singh's condition later yesterday.

No acting prime minister has been named while Singh is in hospital.

Some officials said Foreign Minister Pranab Mukherjee would take over most prime ministerial responsibilities, including defence, security and the finance portfolio, while Singh was recovering from the surgery.

"Pranab Mukherjee is in charge of the government until the prime minister resumes his duty," an official in the prime minister's office, who asked to remain anonymous, told Reuters.

"This is normal procedure as he is the most senior member of the cabinet, so there has been no official announcement."

But a government spokesman insisted this was not the case.

"The prime minister is still in charge," he told Reuters. "Nobody has taken over his functions."

Moily told local media: "There cannot be two prime ministers and under the constitution, there can only be one prime minister."

That confusion was mirrored in the media, where some papers and television channels said Mukherjee was in charge but others disagreed.

"Nobody named in charge," the Mail Today announced on its front page. "No clarity on who controls the nukes. No succession plan leads to ad hocism."

The confusion led to speculation the ruling Congress party did not want to give Mukherjee a public endorsement as acting prime minister just before an election, and overshadow other candidates within Congress battling to be Singh's successor.

Rahul Gandhi, heir to one of India's most powerful family dynasties, is emerging as a potential successor, media reports said.