A social studies teacher barricaded himself inside a classroom at a Georgia high school on Wednesday and fired a handgun, sending students running outside or hunkering down in darkened gym locker rooms, authorities said.

No Dalton High School students were in the classroom when the teacher fired the weapon, and despite the chaotic lockdown and evacuation, the only injury was a student who hurt her ankle running away.

It wasn't immediately clear why the teacher, 53-year-old Jesse Randal Davidson, had the gun. Under questioning by detectives, he refused to discuss what led to the shooting.

The gunfire erupted with a nation on edge two weeks after a Florida school shooting left 17 students and faculty dead and ignited a new debate over gun control in America.

Within minutes of the Dalton shooting, students there took to social media, calling for restricting gun rights.

In the afternoon, President Donald Trump, who has advocated for arming teachers, convened a bipartisan group of lawmakers at the White House to address gun violence.

The teacher was taken into custody without incident after a 30 to 45-minute standoff with officers, police spokesman Bruce Frazier said. A teacher since 2004, Davidson also serves as the play-by-play announcer for the high school's football team.

Police noted that Davidson didn't appear to want to hurt the students or faculty. He fired the gun at an exterior window when the principal tried to enter the classroom.

“I don't know whether he was just firing the gun off to let people know to back off or what,” Frazier said.

The shooting happened about 11:30 am during Davidson's planning period. At first, students tried to get into the classroom, but they couldn't. The students told the principal, who tried to enter.

“I didn't get the door open very far, but he slammed the door and hollered 'Go away, don't come in here.' He had some nonsensical noises that were made as well,” Principal Steve Bartoo said.

Bartoo returned a short time later and put his key in the door “and again he slammed the door before I could open it and he said, 'Don't come in here, I have a gun.'” That's when Davidson fired and the school was placed on lockdown, authorities said.

Davidson faces six charges, including aggravated assault involving a gun and terroristic threats and acts, jail records showed. Other charges include carrying a weapon in a school safety zone and reckless conduct. It's not clear if he has an attorney.

Chondi Chastain told The Associated Press she was supposed to have Davidson's class at 2:30 pm.

“My favorite teacher at Dalton high school just blockaded his door and proceeded to shoot. We had to run out the back of the school in the rain. Students were being trampled and screaming. I dare you to tell me arming teachers will make us safe,” she tweeted in a post that was retweeted 15,000 times within hours.

She said Davidson himself had commented that arming teachers was a bad idea.

“I feel like there just shouldn't be guns at school at all,” she said. “It's our basic student right to feel safe at school and if (teachers were armed), I wouldn't feel safe.”

Student Emma Jacobs texted her mother while she hid inside a darkened classroom, said her mother, Annmarie Jacobs. Emma, a junior, said in texts that her teacher had turned the lights off and told the students to sit in a corner.

Then, in an act that brought home the danger of the situation, Emma texted her mother, “omg she's putting desk in front of the door.”

Nathangel Lopez hunkered down with students and teachers in a gym locker room. While there, he tweeted a photo of teens sitting on benches and called for more gun control.

“This shouldn't happen to us,” he wrote. “I hope a lawmaker somewhere will do something.”

When he found out that a teacher was involved, he shifted his stance on arming educators. “At first, I was thinking that that might have been a good idea. I am now totally against it,” he said.

Several students said on social media they were outraged that some on Twitter questioned whether the incident was staged.

Davidson was described as laid back and smart. In 2012, he was recognised as the school's top teacher, The Atlanta Journal-Constitution reported . He moved to Dalton in 1995 and became sports and news director at WBLJ-AM radio.

“It was always about the students. He really wanted the students to understand the concept,” said 18-year-old senior Rowdy Zeisig.

The principal said Davidson was an “excellent teacher” who was well thought of, and “as far as I know he was fit to be at work.”

Twice in recent years, Dalton police say they encountered the teacher exhibiting odd behavior and wrote in one report that he “may be delusional.”

Davidson had walked into the police department and told a rambling story about thinking a murder had occurred, police wrote in a 2016 report. But police said they investigated and were not able to verify that any of the information was true.

Police said that after the interview, Davidson was taken to a hospital “based on him thinking about hurting himself.”

Police said in another report last year that officers found Davidson during a school day sitting on the curb of a street, conscious but unresponsive and being held up by two school staff members. He was again taken to a hospital.

Both police reports were posted late Wednesday by the Chattanooga Times Free Press.

A week ago, police found a “threatening” note on the floor of a classroom at Dalton High, but it wasn't related to the shooting on Wednesday.

Threats have been made at schools across the country in the wake of the Feb 14 shooting at Marjory Stoneman Douglas High School in Parkland, Florida.

Dalton High has about 2,000 students. The school is about 90 miles (145 kilometres) north of Atlanta.