Elections to two Lok Sabha seats in Andhra Pradesh and 11 Assembly seats in 10 states began on Monday.
Elaborate security arrangements were witnessed in Naxal-infested Karimnagar, which is witnessing a multi-cornered contest with TRS, Congress, BJP and TDP vying for top honours.
In Bobbili, in north coastal Andhra, it is a straight contest between ruling Congress and TDP.
The Karimnagar bypoll was necessiated by the resignation of TDP Chief K Chandrasekhara Rao and the Bobbili bypoll by the death of Telugu Desam Party's sitting MP K Paidithalli Naidu.
In the Chamundeshwari constituency by-poll, there are high stakes as Deputy Chief Minister Siddaramaiah of Congress faces a crucial test of his political career as he takes on JDS supremo and his bete noire Devegowda.
The seat held by Siddaramaiah fell vacant after he resigned from it in June.
The Kota Assembly seat in Chhattisgarh, which fell vacant after the death of Congress veteran Rajendra Prasad Shukla, will be an acid test for former Chief Minister Ajit Jogi's wife Dr Renu, who will face her BJP rival Bhupendra Singh Thakur.
The Dungarpur seat has become a prestige contest for both ruling BJP and opposition Congress with heavyweights such as Chief Minister Vasundhara Raje and her predecessor Ashok Gehlot joining the battle.
Rongjeng by-lection in Meghalaya will see a face-off between ruling Congress in Garo Hills against the backdrop of a fight between chief Minister JD Rymbai and his predeccesor DD Lapang and other party functionaries.
Elections to Assembly seats are also held in Thiruvambadi in Kerala and Manihari in Bihar, Roing in Arunachal Pradesh, Pandhana in Madhya Pradesh, Daryapur and Chimur in Maharashtra and Islampur in West Bengal.