Polling started at 7am amidst tight security arrangements and 23.75% votes were cast in the first four hours of voting, Chief Electoral Officer of UP Umesh Sinha said here.
Maximum 28% votes were polled in Lalitpur, followed by 25% in Jalaun district.
There were reports of voters boycotting the poll process in Etah, Hamirpur and Auraiya districts to protest against lack of development.
Fate of 829 candidates, including that of Leader of Opposition in the state assembly Shivpal Singh Yadav, BJP leader Uma Bharati and former UP chief minister Kalyan Singh would be decided by more than 1.56 crore electorate.
Polling is underway in Firozabad, Kanshiram Nagar, Etah, Mainpuri, Etawah, Auraiya, Ramabainagar, Kanpur, Jalaun, Jhansi, Lalitpur, Hamirpur and Mahoba districts.
The polling is being held at 17,267 polling stations at 11,745 centres. While 2,104 stations have been identified as sensitive, 2,256 have been marked as hyper-sensitive.
To check any irregularity at polling stations, 981 video cameras and 2,100 digital cameras have been installed, Sinha said.
The fifth phase would cover assembly seats in backward Bundelkhand region, bastions of SP and former chief minister Kalyan Singh.
In this phase, Shivpal Singh Yadav is seeking re-election from Jaswantnagar seat in Etawah district.
Fate of firebrand leader Uma Bharati, who is making her debut in UP electoral politics, would be put to test from Charkhari seat in Mahoba district.
Charisma and political strength of former UP chief minister Kalyan Singh would also be tested in this phase when elections would be held in his stronghold of Etah.