Fifty of the 315 children kidnapped by gunmen from a Catholic school in Nigeria's Niger State on Friday have escaped.

The Christian Association of Nigeria says they have been reunited with their families.

A major military-led search and rescue operation is underway for the remaining 265 children and 12 teachers who were taken with them.

Calling for the release of the abductees, Pope Leo XIV expressed "immense sadness" and urged the authorities to act swiftly.

Authorities in several Nigerian states ordered schools to shut following the mass abduction in Niger and another smaller hostage-taking in Kebbi state on Monday, when 20 pupils were kidnapped from a boarding school.

Orders were given for many schools to close in the states of Kebbi, Niger, Katsina, Yobe and Kwara.

News of the children's escape brought welcome relief for families and for a country that has been agonising over the fate of hundreds of schoolchildren abducted in Nigeria's northwest.

According to a Christian group involved in the case, the pupils managed to escape between Friday and Saturday in what is being described as a brave and risky attempt to flee their captors.

The students and teachers were taken from St Mary's School in Papiri, Niger state. Earlier reports spoke of 303 students and 12 teachers being taken.

Their number surpasses the 276 abducted during the infamous Chibok mass abduction of 2014.

Local police say armed men stormed St Mary's at around 02:00 (01:00 GMT), abducting students staying there.

Niger state governor Mohammed Umaru Bongo announced on Saturday that all schools in the area would close, warning that it was "not a time for blame game".

Dominic Adamu, whose daughters attend the school but were not taken, told the BBC: "Everybody is weak... It took everybody by surprise."

One distressed woman tearfully told the BBC that her nieces, aged six and 13, had been kidnapped, adding: "I just want them to come home."

The military, police and local vigilantes are searching for the children, combing nearby forests and remote routes believed to have been used by the gunmen.

Authorities in Niger state said St Mary's School had disregarded an order to close all boarding facilities following intelligence warnings of a heightened risk of attacks. The school has not commented on that allegation.

The kidnapping of people for ransom by criminal gangs, known locally as bandits, has become a major problem in many parts of Nigeria.

The payment of ransoms has been outlawed in an attempt to cut the supply of money to the criminal gangs, but it has had little effect.

On Monday, more than 20 schoolgirls, who the BBC has been told are Muslim, were kidnapped from a boarding school in Kebbi state.

Authorities there have now ordered all secondary schools and colleges to close.

A church was also attacked further south in Kwara state, with two people killed and 38 others abducted.

Nigerian President Bola Tinubu postponed foreign trips - including to this weekend's G20 summit in South Africa - in order to address the security concerns.

This week's attacks follows claims by right-wing figures in the US, including President Donald Trump, that Christians are being persecuted in Nigeria.

For months, campaigners and politicians in Washington have been alleging that Islamist militants are systematically targeting Christians. The Nigerian government has dismissed this claim.

Earlier this month, Trump said he would send troops into Nigeria "guns a-blazing" if the African nation's government "continues to allow the killing of Christians".

The Nigerian government has called claims that Christians are being persecuted "a gross misrepresentation of reality".

An official said that "terrorists attack all who reject their murderous ideology - Muslims, Christians and those of no faith alike".

In the north-east, jihadist groups have been battling the state for more than a decade.

Organisations monitoring violence say most of the victims of these groups are Muslim because most attacks happen in the majority-Muslim north of the country.

In the centre of Nigeria, there are also frequently deadly attacks between herders - who are mostly Muslim - on farmers, who are largely Christian.

However, analysts say these are often motivated by competition for resources, such as water or land, rather than religion.

The militant Islamist group Boko Haram took 276 girls from their school in the town of Chibok in 2014.

The incident drew international attention and sparked a global campaign seeking their return, which included an intervention from then-US First Lady Michelle Obama.

Many have since either escaped or been freed, but as many as 100 remain missing.