Voting for bypolls in 28 Assembly seats in Madhya Pradesh began on Tuesday morning, an official said.
Polling began at 7 am and will end at 6 pm, while adhering to the COVID-19 restrictions, the official said.
The last hour of voting will be for COVID-19 patients and people suspected to be suffering from the disease.
Authorities have set up 250 flying squads, 173 surveillance teams and 293 police check-posts to ensure smooth polling, he said.
Altogether 355 candidates, including 12 ministers, are in the fray, the official said, adding around 33,000 security personnel have been deployed in 19 districts.
There are 63.67 lakh voters in the 28 constituencies and 9,361 polling booths, including 3,038 booths placed under the critical category, he said.
Bypolls for 54 Assembly seats in 10 states are being held on Tuesday and Madhya Pradesh accounts for almost half of these seats.
The by-elections in Madhya Pradesh were necessitated after 22 MLAs of the erstwhile Congress government switched over to the BJP in March 2020, leading to the fall of Kamal Nath's 15-month-old government.
Three other Congress MLAs followed the lead of Scindia and his supporters, and joined the BJP. Another three seats in the Assembly are vacant due to the deaths of incumbent MLAs.
In most of the seats, there is a direct fight between the BJP and Congress, while in two or three seats of Gwalior Chambal region, a triangular contest is on the cards in the wake of the BSP's presence there, political observers said.
Madhya Pradesh Chief Minister Shivraj Singh Chouhan, Union minister Narendra Singh Tomar, BJP's Rajya Sabha member Jyotiraditya Scindia, state BJP chief V D Sharma, and former chief minister Uma Bharti were BJP's prominent campaigners.
State Congress president and former CM Kamal Nath, Chattisgarh Chief Minister Bhupesh Baghel, Congress veteran Digvijaya Singh and party leader from Rajasthan Sachin Pilot toured the state to campaign for Congress nominees.
It is for the first time in Madhya Pradesh that bypolls are being held in as many as 28 Assembly seats in the 230-member House in one go, an official said.
Congress MLAs who quit from 25 seats are now in the fray as BJP candidates. One more Congress MLA resigned recently.
The BJP currently has 107 MLAs, while the Congress has 87 legislators in the House.
The counting of votes will take place on November 10.