The protests against the controversial Act led to major violence in Kanpur, Firozabad's Lalganj area, Bijnor's Naya Bazar area, Bulandshahr, Hapur, Muzaffarnagar, Bahraich and Gorakhpur.
Additional Chief Secretary, Home, Awanish Kumar Awasthi said that five people were killed in the violence.
According to state Director General of Police O.P. Singh, two people were killed in Bijnor, and one each in Meerut, Firozabad and Sambhal. One person had been killed of a gunshot injury in the unprecedented protests in Lucknow on Thursday.
The DGP said that the cause of the deaths would be ascertained as the people were not killed in police firing.
Meanwhile, in view of the situation, the UP TET (Teacher Eligibility Test) examination, scheduled for Sunday, has been postponed. Around 16 lakh people were due to appear in the exam.
Among other incidents of violence, protesters pelted stones at the police, set motorbikes and cars on fire and ransacked police outposts in Hardoi and Farrukhabad.
In return, the police fired tear gas shells and lathicharged protesters.
In Deoband, though, the protests were relatively non-violent.
State Energy Minister and government spokesman Shrikant Sharma appealed to the state's people to maintain peace and urged Muslims "not to allow themselves be used by vested interests, who have been using the community as a political tool since Independence".
The stir across Uttar Pradesh are a part of several such protests that have seized cities across the country since Sunday. Protests were being held in scores of cities including Delhi, Gujarat, Patna, Bengaluru, Mumbai, Bhopal, Thiruvananthapuram, Chennai and Patna.
Security has also been beefed up across the state, as police have registered 19 FIRs against unknown people, of whom 17 are 'named' including Samajwadi Party (SP) leader Shafiqur Rahman Barq in Sambhal district in connection with the violence during Thursday's protest.
At least 3,000 people across the state, including 350 in Lucknow, have been arrested since Thursday night in connection with the violence against the recently amended citizenship law, police officials said on Friday.
A total of 3,037 Facebook posts, 1,786 Twitter posts and 38 Youtube videos (scenes of violence) were deleted since Thursday's protests over the CAA.
Internet services have been shut down in 15 districts, including the capital, even Direct-to-Home (DTH) services were also snapped for sometime, police added.
( With inputs from IANS )