Voting began on Monday in the Congress presidential polls as senior leaders Mallikarjun Kharge and Shashi Tharoor face-off for the post of AICC chief.
Over 9,000 Pradesh Congress Committee (PCC) delegates form the electoral college to pick the party chief in a secret ballot.
Voting began at 10 am at the AICC headquarters here and at party's polling booths in state offices across the country.
Veteran Congress leader P Chidambaram was the first to cast his vote at the AICC headquarters here, sources said.
Kharge is considered the favourite for his perceived proximity to the Gandhis and backing by senior leaders, even as Tharoor has pitched himself as the candidate of change.
During the campaign, even though Tharoor raised issues of uneven playing field, both candidates and the party have maintained that the Gandhis are neutral and that there is no "official candidate".
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While party chief Sonia Gandhi and Congress general secretary Priyanka Gandhi Vadra are expected to vote at the AICC headquarters here, Rahul Gandhi will be voting at the 'Bharat Jodo Yatra' campsite in Karnataka's Sanganakallu in Ballari along with around 40 other 'Bharat Yatris' who are PCC delegates.
Tharoor will cast his vote at the Kerala Congress headquarters at Thiruvananthapuram, while Kharge will do so at the Karnataka Congress office in Bengaluru.
Ahead of the polling, Kharge had said he would have no shame in taking the advice and support of the Gandhi family in running the party affairs, in case he becomes its president, as they have struggled and put their strength for its growth.
The veteran leader had said he is the "delegates' candidate" in these polls.
Tharoor on his part had taken a veiled dig at some senior leaders supporting Kharge, saying some colleagues were "indulging in 'netagiri' and telling party workers" that they know whom Sonia Gandhi wants elected.