A Nigerian man sits on the ground as others queue to cast their vote Saturday in Katsina, Nigeria. A truck bomb aimed at electoral commission headquarters ran into barriers and failed to explode Saturday hours before the start of a Nigerian presidential vote already shadowed by violence, charges of fraud and a last-minute ballot hitch.

Lagos, Nigeria ? A truck bomb aimed at electoral commission headquarters ran into barriers and failed to explode hours before the start of Nigeria’s presidential vote, the national police chief said Saturday.

Voting centers opened despite the attack and the last-minute arrival of some of the 65 million ballots. In a lagoon-side slum in the sprawling city of Lagos where fishermen live in stilt houses, voters dropped their tally sheets into clear plastic boxes. Elsewhere, electoral workers were still scrambling to unpack ballots.

Police Inspector General Sunday Ehindero said that the commission attacker pointed the truck loaded with fuel and gas cylinders toward the headquarters and placed a rock on the accelerator before jumping from the vehicle, which was stopped by barriers and a power pole before reaching the building in the capital, Abuja.

Ehindero called for calm.

“I’m calling on all Nigerians to go about their civil duties … peacefully,” he said.

If successful, Saturday’s election will set up a transfer of power between elected civilian leaders for the first time since Nigeria gained independence from Britain in 1960. Other attempts have been overturned by annulments or military coups.

At least 49 people have been killed since chaotic state elections last weekend and many more were reported dead in earlier political violence. The political opposition has rejected results from the April 14 state elections that showed President Olusegun Obasanjo’s ruling party clearly winning.