"Electioneering gained momentum since Saturday and peaked on Monday as campaign ends on Tuesday evening in all the 15 Assembly constituencies," the official told here.
The by-elections have been necessitated due to the disqualification of the 14 Congress and 3 JD-S) rebel legislators after they resigned from their Assembly seats in mid-July in protest against the former coalition government's poor functioning.
The by-elections will be held in Athani, Kagwad, Gokak, Yellapura, Hirekerur, Ranibennur, Vijaynagara, Chickballapura, K.R. Pura, Yeshwanthpura, Mahalakshmi Layout, Shivajinagara, Hosakote, K.R. Pete and Hunsur.
By-elections in two Assembly segments Muski (Raichur district) and R.R. Nagar (Bengaluru) have been withheld due to litigation in the Karnataka High Court over their results in the May 2018 state Assembly elections.
Vote count is on December 9.
"All our state unit leaders, including Chief Minister B.S. Yediyurappa, three Deputy Chief Ministers G.M. Karjol, Ashwath Narayan and Laxman Savadi and dozen cabinet ministers have been campaigning in all the 15 Assembly segments to ensure the victory of our contesting candidates," BJP's state unit spokesman G. Madhusudhan told .
As many as 165 candidates, including 126 Independents and 9 women are in the fray for the 15 Assembly seats.
The BJP and the opposition Congress are contesting in all the 15 Assembly seats, while the JD-S has fielded candidates in 12 seats, which will witness triangular contests.
In three seats Athani in Belagavi district, Yellapura in Uttara Kannada district and Hoskote in Bengaluru Rural district, the contest will be straight between the BJP and the Congress.
The BJP has fielded 11 former rebel Congress and 3 former rebel JD-S legislators who joined the party on November 14 after the Supreme Court on November 13 allowed them to re-contest though it upheld their disqualification by former assembly speaker K.R. Ramesh Kumar on July 25 and July 28.
The BJP has fielded its former corporate Sarvana from the prestigious Shivajinagara constituency in Bengaluru central.
For the Congress, its former Chief Minister Siddaramaiah, party's state unit chief Dinesh Gundu Rao and other senior leaders, including Mallikarjun Kharge have been campaigning in all the 15 assembly seats.
JD-S supremo H.D. Deve Gowda and his third son and former chief minister H.D. Kumaraswamy have been leading the campaign with other senior leaders and legislators in the 12 assembly segments it is contesting.
"We are not contesting in three seats to avoid dividing 'secular' votes and ensure the victory of the Congress candidates for political reasons," JD-S general secretary Ramesh Babu told .
( With inputs from IANS )