Counting of votes for 38 Parliamentary segments and by-polls to 22 Assembly constituencies in Tamil Nadu began amid tight security on Thursday.
Trends are expected to emerge after about an hour.
The by-polls and Parliamentary elections are crucial for both the ruling AIADMK and main opposition DMK, with the former looking to retain power in Tamil Nadu and the latter eyeing a comeback after consecutive poll setbacks.
Counting of votes is under way in 45 centres across the state, with over 17,000 polling staff and 45,000 police personnel on duty.
As many as 1,520 personnel from the Central Armed Paramilitary Forces and over 38,000 from state police have been deployed on duty.
A total of 88 counting observers are tasked to oversee the counting process.