A second explosion rocked a city in northeastern Nigeria on Saturday with voting set to start in presidential polls, after a first blast the night before, officials said.
"Another explosion in Maiduguri today," said Yushau Shuaib, a spokesman with the national emergency management agency.
"There is also sporadic shooting. Yet to determine if they are politicians, fanatics or armed robbers. Emergency and security officers are moving in to control the situation."
It was unclear if there were casualties.
Late Friday, a bomb exploded near a vote collating centre in the same city, but no casualties were reported, police said.
"There was an attempted bomb attack on an (electoral commission) collation centre for Maiduguri metropolitan last night," state police commissioner Michael Zuokumor told AFP.
"The attackers, who were in a moving car, threw the bomb which exploded about 20 metres (yards) to the office, destroying shops and stalls around. However the office was unscathed," he said.
Zuokumor said no casualties were recorded. Maiduguri was hit by two explosions during parliamentary elections a week ago.
Repeated shootings and other attacks blamed on an Islamist sect have occurred in Maiduguri in recent months, though police have said some of the past incidents may have been politically linked.
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