75-year-old Ansari, whose candidature has been supported by Left parties and UPA allies like SP and BSP, appears set to fend off the contest put up by NDA nominee Jaswant Singh.
As many as 600 electors from an effective electoral college of 787 members of Parliament had cast their vote by 1:00 PM, Ansari's election agent and senior advocate Pravin Parekh said here.
Prime Minister Manmohan Singh, UPA chairperson Sonia Gandhi and Rahul Gandhi were among the early voters in the 14th Vice Presidential election polling for which began at 10:00 AM.
BJD, TDP and RSP have declared that they would abstain from voting. Union Minister Vilasrao Deshmukh is ill and admitted to a Chennai hospital.The three parties together have 34 members in both Houses of Parliament.
With the total number of voting members reduced to 752, the halfway mark for Ansari has become 377. UPA managers claim to have the declared support of nearly 500 members.
BJP leaders L K Advani, Sushma Swaraj, Arun Jaitley, Murli Manohar Joshi, BSP supremo Mayawati and SP chief Mulayam Singh Yadav had cast their ballots before noon.
74-year-old Singh, a former Minister of External Affairs and Finance, has the support of NDA and AIADMK.