Amidst tight security, polling began at 0730 hours on Thursday in byelections to Madhya Pradesh's Gwalior and Sidhi parliamentary constituencies and Udaypura Assembly seat -- the key contest is between the ruling Bharatiya Janata Party and main opposition Congress.

A total of 45 nominees are in the fray for the three constituencies having a combined electorate of 26.35 lakh spread over 2,749 polling centres where electronic voting machines are being used.

Besides the district police and Home Guard personnel, 12 companies each of the Central Reserve Police Force are deployed in Gwalior and Sidhi, while five CRPF companies are deployed in Udaypura, State Election Office sources said.

Polling will conclude at 1630 hours, while votes will be counted at the district headquarters on March 11.

In Gwalior, state Tourism Minister and a member of the Scindia clan Yashodhara Raje is the BJP candidate pitted in a 24-cornered contest with Ashok Singh (Congress) as her main rival. That constituency's electorate comprises 13.78 lakh voters, including 6.35 lakh women.

In the 2004 general election, 40.87 per cent voters exercised their franchise in Gwalior constituency where Ramsevak Singh (Congress) pipped Jaibhan Singh Pawaiya (BJP) by more than 35,000 votes.

In Sidhi, which is Human Resource Development Minister Arjun Singh's native district, Manik Singh (Congress) and the BJP's Kunwar Singh are pitted in a 13-cornered contest.

The electorate comprises 10.90 lakh voters, including 5.22 lakh women. In 2004, the polling percentage was 42.18 and Chandrapratap Singh (BJP) beat Tilakraj Singh (Congress) by a margin of about 50,000.

Gwalior and Sidhi fell vacant as the incumbents were disqualified in the cash-for-query scam.

Eight nominees figure in Raisen district's Udaypura. Vidisha's BJP MP Rampal Singh's wife Shashi Prabha Singh is the BJP candidate and her main rival is Saheb Singh Patel (Congress). The electorate comprises 1.67 lakh voters including 77,000 women.

In the 2003 BJP wave, Rampal Singh vanquished Prakashbhanu Sharma (Congress) by more than 19,000 votes.

Udaypura fell vacant due to R Singh's resignation following his election to the Lok Sabha in the bypoll from Vidisha, which was earlier held by Shivraj Singh Chouhan, who quit after becoming chief minister.

Campaigning in these constituencies was by and large peaceful.