A single night this week revealed the terrifying scope of Nigeria’s kidnapping emergency.

Shortly after midnight on Monday in the northwestern state of Kaduna, gunmen forced their way into a hospital specializing in the treatment of tuberculosis and leprosy and shot three people before kidnapping 10 others, including two infants under the age of two. Less than an hour later, another group of militants broke into the Bethel Baptist school 45 miles away and abducted 121 boys and girls aged between 9 and 16. At around the same time, another group of militants approached the newly renovated campus of Faith Academy and attempted to seize the school’s 500 students, fighting a two-hour running battle with police before withdrawing.

“They took the babies,” said Adamu Jubril, an orderly at the National Tuberculosis and Leprosy Centre in Zaria, who cowered next to a window and watched the assailants drag away the screaming hostages. “It makes the families pay the ransom quicker.”

The attacks, conducted within hours of each other, spotlight the terrifying frequency of what has become a routine and brutal business in Africa’s most populous country.

Footwear of the abducted students of Bethel Baptist High School.

Footwear of the abducted students of Bethel Baptist High School.

Photo: stringer/Reuters

Since December, heavily armed criminal gangs have abducted and ransomed more than 1,000 children in attacks on 11 school dormitories, rocking Nigeria and drawing calls for urgent action from the U.S. government, the European Union and Pope Francis. Hundreds of school campuses have been closed across four states for fear of more attacks, leaving close to 15 million Nigerian children out of school—more than any other country in the world.

Now, the abductions are mushrooming to include other targets that would normally be seen as havens, including hospitals. Politicians and celebrities have also been snared. Last month Nigeria’s longest-serving soccer coach Stanley Eguma was abducted, while Ahmad Ahmad, a member of the state house of assembly in northwestern Zamfara state, was killed during a botched kidnap attempt.

Doctors in northwestern states say they can only do their rounds safely if guarded by armed police. Families rush into wards to remove bedridden family members after hearing rumors the hospital could be a target. Once-busy expressways connecting trading towns have become virtual no-go zones because bandits erect mobile checkpoints and abduct the travelers, local officials say.

“Our region is under siege…What is happening here is so disturbing,” said Ahmed Nuhu Bamalli, the Emir of Zuzzau, a traditional ruler in the northwest. “When my district heads come to report on the security situation, they are often crying.”

The statistics paint a grim picture of an exploding kidnap-for-ransom economy.

Since January, a record 3,000 people have been abducted across Nigeria, according to Statisense, a Nigerian data company, including 1,344 people in June alone. That is a total of 45 people kidnapped each day. More than 300 are still missing and the true toll is far higher since so many attacks go unreported. More than $18 million has been paid out by Nigerians in ransom over the past decade, according to a report from Lagos-based risk-analysis firm SB Morgan Intelligence.

Damage from a kidnapping attack by militants at Bethel Baptist High School.

Damage from a kidnapping attack by militants at Bethel Baptist High School.

Photo: AP Photo/Associated Press

The kidnap crisis—which comes as Nigeria is facing its worst recession for four decades—is spreading from its epicenter in the northwest of the country, where criminal gangs carry out kidnappings, exploiting the ineffective government and weak security presence. They are dominated by nomadic herders from the Fulani ethnic group, who have been feuding with farmers over access to grazing land for their cattle. The clashes have become increasingly violent, and about 4,000 people have been killed in fighting since 2015, according to another SBM Intelligence report.

On Tuesday, a day after the three mass-kidnap attempts, 21 people were killed in multiple raids on villages in the neighboring state of Katsina. The state governor, Aminu Bello Masari, last week became the latest Nigerian political leader to call on citizens to take up arms to defend themselves, as law and order appears to be breaking down.

“Security issue is our responsibility; we do not have to surrender ourselves and expect others to fight for us,” Mr. Masari said.

From the Archives

Teenagers Binta Umma and Maimuna Musa were kidnapped by Boko Haram in Madagali, Nigeria, in 2016. They were forced into marriage and sent to die on a suicide mission. In this video, the girls tell the story of their survival. Photo by Jonathan Torgovnik for The Wall Street Journal The Wall Street Journal Interactive Edition

Nigeria’s population appears to be both stunned and numbed by the near-daily headlines of attacks against children and other soft targets.

To raise ransoms to retrieve their children, thousands of Nigerians are losing everything: liquidating their assets, selling off their homes and farmlands or incurring huge debt

“Just when you think it won’t get any worse it proves you wrong,” said Bulama Bukarti, a Nigerian human-rights lawyer and analyst at the Tony Blair Institute for Global Change. “Huge parts of rural Nigeria have become completely ungovernable. There has never been a more trying time to be a Nigerian.”

Demonstrators in Abuja, Nigeria, called for the release of abducted students in May.

Demonstrators in Abuja, Nigeria, called for the release of abducted students in May.

Photo: kola sulaimon/Agence France-Presse/Getty Images

Kaduna state governor Nasir Ahmad El-Rufai has been one of the most vocal political leaders calling for other officials to stop paying ransom money, echoing a call by President Muhammadu Buhari. Yet Mr. El-Rufai was forced to withdraw his own children from public schools in Kaduna last month, citing three credible plots to abduct his son, Abubakar.

The kidnappers, known as bandits in Nigeria, are criminal groups who have become sophisticated and well-armed, using the dense Rugu Forest, which spreads across four Nigerian states and several hundred square miles, as a hiding place and base from which to launch attacks and then hold captives.

The epidemic of insecurity in those areas comes after a decade of state breakdown in the northeast, where jihadist group Boko Haram, whose name roughly translates as “Western education is sinful,” began the attacks on schools after it declared war on the Nigerian state in 2009.

Boko Haram kidnapped thousands of children as conscripts, but the mass abduction that drew international attention was its infamous kidnapping of 276 schoolgirls from the town of Chibok in 2014, igniting the global #BringBackOurGirls campaign.

More than 100 of those captives were freed in two exchanges in 2016 and 2017 for a prisoner swap and a ransom of 3 million euros, or about $3.6 million, according to government officials and people involved in the negotiations. Seven years after the kidnapping, more than 100 are still missing.

Smoke billowed from protests near Abuja in May against the kidnapping and killing of residents.

Smoke billowed from protests near Abuja in May against the kidnapping and killing of residents.

Photo: kola sulaimon/Agence France-Presse/Getty Images

Oby Ezekwesili, the former education minister who led the #BringBackOurGirls campaign, said on Wednesday that her worries about what the Chibok abduction could herald had been realized: “It was fear of what could happen to our children and their education if our government and entire society failed to send a strong signal that we value our young citizens…That fear was valid.”

Monday’s attacks represented a grim new threshold.

Mr. Jubril remembers looking at his watch when he was waked by the sound of gunfire around the hospital’s staff dormitory. “It was 12:57 and I could see armed men everywhere,” he said. “They were shouting into the buildings for people to come out.”

Hospital officials said the gunmen were looking for the senior doctors but when they failed to find them, they ordered staff and patients away at gunpoint. One of those kidnapped was Christiana Afalu, along with her two daughters, 12-year-old Maranatha and Bethel, just a few months old.

“I saw the women carrying the babies. Everyone was terrified,” Mr. Jubril said.

As gunmen were raiding the hospital compound, another gang of kidnappers were barging into the boardinghouses at the Kaduna Baptist Bethel School 50 miles away, demanding students gather in the darkness. Dozens of armed men on motorbikes had arrived at the school after midnight, while the students were sleeping, as another group attacked a nearby police station. More than 120 children were marched into the forest and are still missing. Rahela John’s youngest daughter Banat, 10, is among them. “I can’t sleep. I can’t do anything,” she said, her voice quivering. “I love her so much.”

On Tuesday night, 24 hours after the hospital abduction, Christiana’s husband, Hassan Afalu, got a call to say his family had been abducted.

“The kidnappers called me last night and demanded 10 million Naira (equivalent to around $25,000) but I told them I don’t have that kind of money and asked if they’ll take 500,000,” he said. “They refused, said I’m not serious and that I should call back when I am.”

Write to Joe Parkinson at joe.parkinson@wsj.com