Updated 6.20pm

A shooting on Thursday at a high school in the midwestern US state of Iowa left "multiple gunshot victims," local authorities said, adding the incident was over but without confirming if anyone had been killed.

The shooting at around 7.30am (1330 GMT) triggered a major police response as emergency vehicles and armed units rushed to the Perry High School, where classes had not yet started for the day.

"We are still unclear exactly how many are injured or what the extent of those are, but we are working on that right now. There is no further danger to the public," Dallas County Sheriff Adam Infante told reporters gathered at the school.

Broadcaster NBC reported that the shooter died from a self-inflicted gunshot wound, citing multiple law enforcement officials.

"An officer first arrived within seven minutes of (a radio) activation and located multiple gunshot victims," Infante said.

He said that there were "very few students and faculty in the building, which I think contributed to a good outcome, in that sense."

He added that the authorities had identified the shooter, but didn't give any further details, including on any arrest or deaths.

"The community is safe. We're just now working backwards, trying to figure out everything that happened," Infante said.

CNN reported that Thursday was scheduled to be the first day of classes for the new semester, according to the school district's calendar.

Perry is about 55 kilometres from the state capital, Des Moines.

Plagued by school shootings

Gun violence is common in the United States, a country where there are more firearms than people, and where attempts to clamp down on their spread are always met with stiff political resistance.

The country has already recorded three mass shootings this year, according to the Gun Violence Archive, a nongovernmental organization that defines a mass shooting as four or more people wounded or killed.

Last year ended with a total of 656 such shootings.

School shootings in particular have become a totemic reminder of the country's political deadlock.

In May 2022, a man killed 19 students and two teachers at an elementary school in Uvalde, Texas.

The Perry shooting comes less than two weeks before the Iowa caucus, the country's first contest kicking off the primary season for the 2024 presidential election.

Guns are likely to once again be a hot topic of debate this election cycle, though with little legislative action expected.