Gunmen attacked a Catholic church in southwest Nigeria during mass on Sunday, killing at least 50 people including women and children, according to a hospital doctor and media reports.
The gunmen shot at people outside and inside the church building, killing and injuries worshippers, said Funmilayo Ibukun Odunlami, police spokesperson for Ondo state.
She did not say how many people were killed or injured at St Francis Catholic Church in the town of Owo but added police were investigating the cause of the attack.
Ondo state Governor Arakunrin Oluwarotimi Akeredolu, who visited the scene of the attack and injured persons in hospital, described Sunday's incident as "a great massacre" that should not be allowed to happen again.
"It is so sad that while the Holy Mass was going on, unknown gunmen attacked St Francis Catholic Church...leaving many feared dead and many others injured and the Church violated," said Catholic Church spokesman in Nigeria, Reverend Augustine Ikwu.
Ikwu said the bishop and priests from the parish had survived the attack unharmed.
A doctor at a hospital in Owo told Reuters that at least 50 bodies had been brought into two hospitals in the town from the attack. The doctor, who declined to be named because he is not authorised to speak to the press, also said there was a need for blood donations to treat the injured.
"Immediately they entered and started firing everywhere, so many people," said Alex Michael, who was shot in the leg while protecting his children by hiding them under chairs. He appeared dazed as he sat on his hospital bed.
Around him were other survivors, many with limbs wrapped in bloodstained bandages. One man writhed and moaned on his bed, while a woman wept as she embraced her brother. A 15-year-old victim lay silently with a drip in his hand.
Dr Samuel Aluko, a registrar at the hospital, said 27 adult victims were receiving treatment in his department for a wide range of injuries, some of which were life-threatening. He said one woman had lost both legs.
Medical director Dr Ahmed Lasu said 13 children had been rushed to the hospital, of whom two were dead on arrival.
Speaking to Premier Christian News,CEO of Humanitarian Relief Aid Trust, Baroness Cox said the attack is part of Islamists trying to "eradicate Christianity" from Nigeria.
"Islamists, Boko Haram and Islamist Fulani, they are quite explicit that they want Christians out of Nigeria. ISIS is there in Nigeria, and they are wanting to eliminate Christianity from Nigeria."
She also said Christians worldwide have a responsibility to pray and help those persecuted for their faith.
" As far as Christians concerned, as St Paul said at the church in Corinth, when one part of the body of Christ suffers, we all suffer. But many Christians just don't know what's going on in Nigeria, so do not suffer with the Nigerians and they [Nigerians] do not receive the help that they desperately need: prayer support and practical support aid"
The Catholic bishop of the diocese of Ondo, Jude Ayodeji Arogundade, said he had rushed to the church just after the attack.
"It was beyond what I ever imagined. A lot of bodies right there in the church, blood-soaked bodies," he told AIT television channel.
Pope Francis and Nigerian President Muhammadu Buhari were among those who expressed horror on Sunday.
Ondo State Governor Arakunrin Akeredolu on Monday directed that flags in the state should be flown at half-mast for seven days.
Vice President Yemi Osinbajo and former Lagos State governor Bola Tinubu, the frontrunners in the ruling party's primaries to select its presidential candidate for next year, both headed to Owo to offer their condolences.