The Lok Sabha seats where polling is being held include Kairana in Uttar Pradesh, Palghar and Bhandara-Gondiya in Maharashtra and the sole parliamentary constituency in Nagaland.
Assembly bypolls are taking place in Noorpur in Uttar Pradesh, Shahkot in Punjab, Jokihat in Bihar, Gomia and Silli in Jharkhand, Chengannur in Kerala, Palus Kadegaon in Maharashtra, Ampati in Meghalaya, Tharali in Uttarakhand and Maheshtala in West Bengal.
Voting is also underway in Raja-rajeshwari Nagar constituency in Karnataka.
The Election Commission had on May 11, postponed polls to the R.R. Nagar Assembly constituency from May 12 to 28 following an inquiry into the seizure of around 10,000 voter identity cards. Counting for all the seats will take place on Thursday.