Shehu Sani, the President of Civil Rights Congress based in Kaduna, said two explosions took place at the Assemblies of God's Church near the centre of the city with a large Christian population and known as a major cultural and economic centre in Nigeria's north.
“There were two explosions and the casualty figure may go up because some injuries were really critical,” he said on phone.
Another resident of the city, Miss Blessing Audu told PTI that the explosion has caused panic among Christians celebrating Easter.
She said some parts of the church were damaged even as the vibration caused by the explosives were heard in several parts of the city.
An emergency worker on condition of anonymity explained that the bombs were planted in two cars near the church. At least 50 people were killed amid fears that the casualties may rise from the blasts.
He said his agency has been able to recover 20 bodies from the site.
Police spokesman Aminu Lawal confirmed the incident to PTI but sought more time before making a formal statement. Ahead of Easter celebrations, the US and the UK had warned of possible bomb attacks, advising its citizens against travelling to certain parts of the country.
No one has yet claimed responsibility for the bombings, but the BBC reported that Boko Haram recently said it would carry out attacks in the area over the Easter holiday.
The radical group has carried out a series of attacks on churches and other locations on Christmas Day, including outside the church in capital Abuja, where 44 people died.
It is waging a bloody war against the government to seek the enforcement of strict Shariah law and the release of all its detained members.
The group has bombed churches and attacked mosques in the 150-million nation that has both Muslim and Christian population, with Muslims predominant in the north while Christians mostly living in the South.
Coordinated multiple bombings and gun attacks in the northern city of Kano by Boko Haram cadres killed 185 people, including an Indian from Gujarat on January 20. A suicide bomb attack by the group at the United Nations headquarters in Abuja in July last year killed 26 persons.