Prime Minister Manmohan Singh, several union ministers and Congress leaders stood in rapt attention as All India Congress Committee president Sonia Gandhi unfurled the party flag to celebrate the party's 121st foundation day on Thursday.
Gandhi then joined Seva Dal activists and others in singing Vande Mataram and the national anthem.
After a salute to the party flag, Gandhi walked up to Dr Singh to greet him on the party's foundation day. She went about greeting ministers and party leaders who had come from across the country.
Gandhi also held a brief meeting with the leadership at her office in the party headquarters.
Later, Gandhi and Dr Singh walked up to the journalists and greeted them for the new year in advance.
The gathering then dispersed for tea where discussions centred round observance of the centenary of the Satyagraha started by Mahatma Gandhi a hundred years ago in South Africa.
The Indian National Congress was founded by Scotsman Allan Octavian Hume on this day in 1885.
The first session of the party, held at Mumbai between December 28 and December 31, was attended by 72 members. Womesh Chandra Banerjee was its first president.