Gunfire opened Nigeria's delayed election day today as President Muhammadu Buhari seeks a second term in Africa's most populous nation. Police said, the blasts in Borno state capital, Maiduguri, shortly before the polls opened were for security purposes in a show of force to deter the Boko Haram extremists.<br />''<br />''Gunfire also was heard in parts of Port Harcourt in the restive south, where the group's presence was said to be heavier than in past elections.<br />'' <br />''In a field of 73 presidential hopefuls, the two front-runners include incumbent Buhari and former vice-president Atiku Abubakar. <br />''<br />''Electors are also choosing 360 members of the House of Representatives and 109 senators from a choice of 6,500 candidates.<br />''<br />