The bomb -- "most likely carried by a suicide bomber" -- exploded at a local government council's office in the Sabon Gari section of the city of Zaria, Kaduna state Gov. Nasir El-Rufai said.
Nigeria's National Emergency Management Agency reported that 26 people died and another 33 were wounded. The agency urged citizens to donate blood for those hospitalized.
The building was crowded because residents were welcoming the new chairman of Sabon Gari's interim management committee, El-Rufai said. That leader was taking office Tuesday, and other civil servants were being registered at the building.
A 2-year-old child was among the dead, the governor said.
After the attack, authorities ordered "all beggars and hawkers ... to stay off the streets until further notice," said Kaduna state government spokesman Samuel Aruwan.
"Any beggar or hawker found on the streets will be arrested until these measures are relaxed. In addition, (the) government reiterates that the ban on motorcycle taxis remains in force."
El-Rufai said extra security forces would be deployed throughout the state. An official statement from the state government called the attack "mindless."
"We call on our citizens to be vigilant and avoid crowded places like markets, mosques, churches and motor parks in the next few weeks," El-Rufai said on Twitter following the incident.
A bloody July in northern Nigeria
Northern Nigeria has seen near-daily attacks on civilian and government targets since last week, leaving more than 200 dead. Witnesses and government officials have blamed last week's attacks on Boko Haram, the terror group that has been fighting the Nigerian government for more than a decade, pushing to bring an extreme version of Islamic law, or Sharia, to the masses.
No group immediately claimed responsibility for Tuesday's attack in Zaria.
A summary of northern Nigeria's bloody July:
• On July 1, Boko Haram fighters raided villages in northeastern Nigeria's Borno state
, killing more than 150 people, witnesses and government officials said.
• On Sunday in Jos state, just east of Kaduna, an explosion ripped through a restaurant full of customers in a shopping complex. Also in Jos that day, attackers shot at a crowded mosque before launching a rocket-propelled grenade at the building. At least 44 people were killed and 47 others were injured in the pair of attacks
, said Mohammed Abdussalam, an official at Nigeria's National Emergency Management Agency. No claims of responsibility were immediately made.
• On Sunday in the city of Potiskum in Yobe state, a suicide bomber blew himself up in a church
, killing the priest and four other worshippers, witnesses and police said.
• On Monday in the city of Kano, explosives carried by a 13-year-old female suicide bomber detonated near a mosque. The girl died; no one else was hurt, police said.
Nigerian President Muhammadu Buhari on Friday called last week's attacks "inhuman and barbaric" and pledged that every last "Boko Haram bandit ... would be hunted down without mercy and compromise."
Elected earlier this year, Buhari vowed to focus on the fight against the terrorist group, which has pledged allegiance to ISIS. But so far, he has struggled to stop the heavy bloodshed in the Northeast.
Along with suicide bombings, Boko Haram has attacked churches and mosques, raided once-peaceful villages and kidnapped people young and old, most infamously more than 200 girls taken in April 2014 from a school in Chibok
Boko Haram's strongest presence is in northern Nigeria, where the majority of the country's Muslims live. The country's south is largely Christian and animist.