Premier Manmohan Singh and Gandhi's daughter-in-law Sonia, leader of the ruling Congress party, who cradled Indira in her arms as she was dying, were among those who paid their respects at memorial sites around New Delhi.

Sonia Gandhi's son Rahul, a key force in the Congress party and seen as a potential prime minister, solemnly sprinkled flower petals on a monument dedicated to his grandmother, where multi-faith prayers also took place.

Visitors queued up to visit Indira Gandhi's sprawling white bungalow residence, which was turned into a museum after the leader, known as India's "Iron Lady," was gunned down by her Sikh bodyguards in 1984.

"In our country there is no one like her," one man told the CNN-IBN network.

"She worked so hard but had to suffer," said another visitor.

Congress asked members to observe two minutes silence to mark the death of Indira Gandhi, one of the Nehru-Gandhi political dynasty that has dominated Indian politics for most of the years since India's independence in 1947.

Deadly anti-Sikh riots followed Gandhi's killing which was in revenge for her decision to send in the army to evict Sikh separatists from the religion's holiest site, the Golden Temple, in Punjab.

The state was racked by a violent insurgency at the time.

Indira's son Rajiv Gandhi, who was himself slain by a Tamil Tiger bomber in 1991, was widely criticised for seeming to downplay the violence when he said, "there are always tremors when a great tree falls."

Only a handful of police officials have been punished and none of the Congress leaders accused of inciting the mobs have been successfully prosecuted.

Newspapers ran retrospectives recalling Gandhi, India's only female prime minister, who spent more than 15 years in office.

"A grateful nation will never forget your sacrifice," declared an ad placed by the petroleum ministry, one of several government departments that funded notices honouring Gandhi.