Details were unclear about Saturday's explosion in the northeastern city of Maiduguri, scene of repeated violence in recent months blamed on an Islamist sect, and came as Nigerians shook off fears over Friday's bombing to cast votes.
"There was no death as of now," said emergency management agency spokesman Yushau Shuaib. "Only injuries and victims taken to hospital ..."
An electoral commission spokesman confirmed the explosion in Maiduguri but could not immediately provide details.
The blasts and repeated vote postponements have marred efforts to organise a credible ballot in Nigeria after years of violent and deeply flawed polls. But many voters standing in line at polling stations said they were determined to see change.
Polling stations in many areas of Africa's most populous nation had opened at or near the scheduled start time, in stark contrast to the week before, when organisational chaos led officials to pull the plug at around midday.
However, some areas started late, and the election was postponed in Suleija, the area near the capital Abuja hit by Friday's bomb blast that killed at least 11 people and wounded 38 in an attack President Goodluck Jonathan called "heinous".
No one had claimed responsibility for the blast, which occurred as electoral workers, including members of the national youth service corps, made final preparations.
Despite the violence, there was a strong willingness across the country to cast ballots in the vote, the first of three landmark elections this month.
From the economic capital Lagos, a city of some 15 million people in the southwest, to the country's second-largest city of Kano in the north, voters said they turned out because they saw this year's election as an opportunity to break with the past.
"I have voted a few times, but I have never seen as much voter turnout as this time," said Usman Shehu, a 35-year-old banker among thousands seeking to vote at a polling place in a densely populated area of Kano.
Jonathan's voting station in his home state of Bayelsa in the oil-producing Niger Delta region was among those that did not function a week ago, but on Saturday it opened about 90 minutes after the scheduled start time.
Before voting there, Jonathan said "there are some anti-social elements that want to derail the process of voting, but they will not succeed."
The effect that the postponements and blasts would have on final turnout was not yet clear, with there appearing to be fewer voters than the week before in some areas but more in others.
A lawyer at one Lagos polling station Saturday morning said the blast in Suleija should not be allowed to mar the vote. An electoral official at the same polling unit said "they are trying to instill fear into us, but it will not work."
"Nigeria cannot be turned into another Afghanistan or Iraq," said Nnamdi Ekweogu.
A number of incidents were also reported in the Niger Delta -- notorious for election fraud and violence in the past -- including the hijacking of vote materials and personnel in one troubled area of Bayelsa state, an electoral official said.
The presidential election is set for April 16, with Jonathan the favourite and his main challenger seen as ex-military ruler Muhammadu Buhari. Governorship and state assembly ballots are set for April 26.
Tremendous hopes have been placed in a respected academic appointed in June to head the electoral commission, and he has been under intense pressure to deliver.
His decision to pull the plug on parliamentary polls on April 2 hours after they were due to begin, with material and personnel failing to arrive in a large number of areas, at first drew outrage.
But he has since received numerous expressions of support, including from the president, with many arguing it was better to call it off rather than push ahead with a vote that could never be considered credible.