A wave of fake reports of shootings sent several Minnesota schools into lockdown Wednesday, authorities said.

The Minnesota Bureau of Criminal Apprehensions (BCA) said the hoax calls were reported in more than a dozen districts, including schools in Minneapolis, St. Paul.

The calls also were reported in Rochester, Mankato, Austin, St. Cloud, New Ulm, Fairmont, Alexandria, Fergus Falls, Brainerd, Grand Rapids, International Falls, Bemidji and Cloquet. On Wednesday evening, a bomb threat was called into Coffman Memorial Union at the University of Minnesota, although the BCA said Thursday that it though that incident was unrelated.

"Given that number, I wouldn't doubt there's even more than that," BCA Superintendent Drew Evans said. Rosemount school district was the target of a hoax call earlier in the week.

The calls claimed there was an active shooter or mass casualties in classrooms. All reports were similar in nature — they come from an internet-based phone number with an out-of-state area code. None was real.

After the calls, local police in each district searched the schools. Meanwhile, school officials called or emailed parents informing them of the hoaxes and encouraging students to report any suspicious activity to law enforcement.

Minneapolis Public Schools officials said police searched Washburn High School after a hoax report of an active shooter. St. Paul police responded to a similar report shortly after noon at Johnson Senior High School, where they met with staff before sweeping the building. In St. Cloud, police searched Apollo High School.

About 10 a.m. in Rochester, a caller reported a man armed with a rifle was shooting people inside Lourdes High School. City police and Olmsted County deputies searched the Catholic school, where most students were in convocation at the time.

"This is just a despicable act," Sheriff Kevin Torgerson said at a news conference shortly after the lockdown at Lourdes was lifted. "It just really makes me sad to know that somebody would be willing to do this."

Swatting involves making a prank call to law enforcement in an attempt to bring a large police response to a particular address.

The hoax calls followed similar "swatting" attempts across the U.S. in the past few weeks as students begin a new school year. Dozens of schools in at least 11 other states have dealt with shooting hoaxes since Sept. 13, according to the National Association of School Resource Officers (NASRO).

"We have to treat every reported incident seriously, as if it's real until we know it's not," Evans said.

Law enforcement experts say it's key to keep communication open between school officials and police during a shooting incident, even if it's a hoax.

Mac Hardy, director of operations with the NASRO, said schools may need to change their safety plans to account for future swatting, just as schools have adjusted fire and active shooter drills over the past few years.

"This is a relatively new phenomenon, and we have to tackle it quickly," he said. "We can't wait."

Several Lourdes students said the situation made them anxious as they didn't know what was happening at first. "It was very fortunate where we were at the time," sophomore Jaylen Mwanza said.

Makena Nyokai was at home sick when her sister called her crying, saying there was a shooter at the school. She picked up her two children at Lourdes around noon after the lockdown was lifted.

"I was very, very shaken," she said. "I had my sons texting me, telling me they were very, very scared and very distressed."

In Cloquet, about 20 minutes southwest of Duluth, a 911 caller reported an active shooter at the high school shortly before 11 a.m., giving a room number as the site of the shooting.

Police responded immediately, said Cloquet schools Superintendent Mike Cary, and found the report false — the room number didn't exist at the school. The high school and adjoining middle school were locked down for about 30 minutes as police swept both buildings. Parents were notified, and many picked up their children midday, Cary said.

"It's amazingly disruptive when this happens," he said, recalling a hoax bomb threat called in about the high school last spring.

About 40% of the school's students either go home for the day or don't come to class the next day if the hoax occurs at night, he said.

"In my personal opinion, if we were serious about this, we would be looking legislatively … on how we can curtail people dialing in from unidentified phone numbers and calling in false claims," Cary said.

At the University of Minnesota, police responded to an individual who claimed to have a bomb, according to Jake Ricker, director of public relations at the school. About an hour later at 7 p.m., the building and surrounding area was safe to return to, according to an alert from the university.

Staff writers Jana Hollingsworth, Eder Campuzano and Alex Chhith contributed to this report.

Correction: Earlier versions of this story included Rosemount as a target of a swatting hoax on Wednesday, citing the Bureau of Criminal Apprehension. The BCA clarified Thursday that the school district was targeted earlier in the week.