Ibadan, Nigeria (CNN) -- Separate bomb blasts ripped through a polling station and a collation center in northeastern Nigeria Saturday as Africa's most populous nation began voting in elections marred by violence and delays.
The first explosion occurred at a voting station in the city of Maiduguri, National Emergency Management Agency spokesman Yushau Shuaib said. No deaths were reported; the number of injuries was still unknown.
The second blast was also reported in Maiduguri, at the Abba Ganaram collation center, Shuaib said, adding that the explosion caused "serious casualties." It was not immediately clear how many people died.
Also in Maiduguri, armed youths set a government building afire, Shuaib said.
A new election chief promised "free and fair" elections this year, but the election has already been plagued by related bombings, assassinations and logistical problems that delayed the vote. Concerns are that continued violence could derail the vote altogether.
Nigerians began voting Saturday for 360 House of Representatives seats and 109 Senate seats. The staggered voting structure will take them back to the polls next Saturday to vote for a president and on April 26 for a gubernatorial vote.
Despite domestic and international pressure, Nigeria's Electoral Commission was forced to put off elections by a week after a nationwide logistical disaster -- many voting materials were not even in the country until voting day and party logos were missing from ballot papers.
It was a huge setback, reminiscent of the problems of Nigeria's 2007 elections, described by the European Union as the worst it had seen anywhere in the world with rampant vote rigging, violence, theft of ballot boxes and intimidation.
The legitimacy of the country now rides on the three rounds of polling.
On the eve of the vote, a bomb exploded at the Independent National Electoral Commission office in Suleja in central Nigeria, officials said.
A government official, who was not authorized to speak on the record, told CNN that eight people died in the attack.
Shuaib said more than seven people were seriously injured.
"We condemn this cowardly and dastardly action, which seems designed to instill fear in Nigerians and paralyze their aspirations for peaceful and credible elections," the chairman of the electoral commission, Attahiru Jega, said in a statement. "Our deep sympathies go to the families of all these young Nigerians who lost their lives or were injured."
Human Rights Watch estimates that at least 85 people have been killed in political violence so far.
As Africa's most populous country and its largest oil producer, Nigeria is important. Yet, despite its enormous oil wealth, 80% of the population lives on less than $2 a day, according to the United Nations.
"Make no mistake about it: This test of honour is inescapably a collective one for all Nigerians," the Independent National Electoral Commission said in a recent statement. "It is our national honour at stake, and our relevance in the affairs of the modern world being redefined."
Separately on Friday, one man was killed and another seriously injured in a blast in the northern city of Kaduna, state news reported.
Police rushed to the scene and found unexploded dynamite there, according to the Kaduna State Police Commissioner Haruna John, Voice of Nigeria reported. They found more dynamite at a house belonging to he injured man, the outlet said.