At least 25 people lost their lives and 32 others were wounded following the attack in Zaria, according to Nasir El-Rufai, the governor of Kaduna state.
Mr El-Rufai said a two-year-old was among the victims of the attack in the office, and called on people to avoid crowded places as Nigerian authorities look to crack down on the terror threat.
No group has claimed responsibility for the atrocity, but it comes after Boko Haram, the militant Islamist organisation, ramped up its attacks since president Muhammudi Buhari came to office in May.
Witnesses in Zaria said the suicide bomber struck in a building where workers, including teachers, had been lining up in hope of gaining employment. The attack took place at about 8am yesterday in the city’s Sabon Gari district while public sector workers were queueing for identity checks.
Eyewitness Mohammed Abubakar, who had been waiting outside at the time of the attack, said: “We were taking turns going into the hall in batches for the screening and also to get our pay cheques. The first batch had gone in. There were almost 100 people there, including the staff, the screening committee and accountants from the banks.
“There was a huge explosion inside the hall followed by billows of smoke and dust. Now the area has been cordoned off by security men. I can’t give you an exact toll but I believe that dozens must have died given the number of people inside and the sound of the explosion.”
Mr El-Rufai said: “I am sad to confirm that an improvised explosive device most likely carried by a suicide bomber exploded in Sabon Gari and killed 25 people, including a two-year-old.
“We call on our citizens to be vigilant and avoid crowded places like markets, mosques, churches and motor parks in the next few weeks.”
The bombing came a day after Nigeria’s police force announced increased security around mosques and churches after Boko Haram assaults on Sunday killed more than 60 people in a mosque and a Muslim restaurant in central Jos city, and at an evangelical Christian church in Potiskum, to the north-east of the country.
The wave of measures announced by police chief, Solomon Arase, include the banning of street trading and hawking in the capital, Abuja, and increased security at mosques and churches throughout the country.
Some analysts say the increased terrorist activity is linked to Mr Buhari’s decision to remove military checkpoints, arguing that internal security was the responsibility of the police.
That move has been criticised by Simon Lalong, the governor of Plateau state, who warned that checkpoints restrict the movement of militants in and around the country.