Authorities and the police refused to give the details but National Emergency Management Agency spokesman Yushau Shuaib confirmed that there were casualties.
In southern state of Osun where pockets of violence also defaced the elections held after an initial rescheduling from April 2, a man was arrested by the police after an alleged ballot snatch. A pump action rifle and large amount of money were found in his possession.
Ballot boxes were reportedly snatched at Victoria Island in southwestern commercial hub of Lagos while in Adamawa, the police apprehended a man with 500 ballot papers.
In the morning, polling stations around the country were besieged by crowds of voters anxious to cast their ballots.
Despite bomb blast that claimed five lives at an Independent National Electoral Commission`s office in northern Niger state, enthusiastic eligible voters could be seen at several polling units in the country`s commercial capital of Lagos.
"We have completed accreditation and preparing for the voting," a voter, Leke Babatunde, told PTI at Ikotun area of Lagos displaying a finger with ink mark.
Bukola Olaniran, a polling officer who is on National Youth Service Corp - a compulsory one year military service for college graduates - said unlike last Saturday they have been given enough materials to conduct the exercise today.
However, in northern state of Kaduna where three polling officers and a politician were shot dead yesterday, a voter Irene Ogbuwa said that situations are more serene than last Saturday.
Military rule ended in Nigeria in 1999 and the oil rich African country has held elections every four years but international observers have described them as flawed.
The polls will be followed by presidential elections on April 16 and governorship on April 26.
Fifteen senatorial districts and 48 federal constituencies will not participate in the present election but would have to wait till April 26, the same day governors will be elected.
Land borders have been closed to forestall any interference by foreigners in the elections just as some aliens from neighbouring Niger Republic were sent home after being found with voting materials.
A bomb blast yesterday hit an electoral office in central Nigeria, killing at least 11 people.