At least seven children and two adults have been killed and over 20 more injured in a mass shooting at a school in the Russian city of Kazan, according to local authorities.

A gunman attacked school no. 175 in the city about 500 miles east of Moscow on Tuesday morning while hundreds of children were in classes. Police said they were able to detain the alleged shooter, a 19 year-old man, at the school.

Videos from the scene showed children trying to flee the school building, with some jumping out of high windows as the sound of gun shots rang out. Heavily armed police and emergency workers descended on the scene and videos showed terrified children climbing down fire ladders to escape. Other videos showed some children lying in grass near the school covered in blood.

“It’s a great tragedy. We have lost seven children, four boys, three girls. They died here on the third floor,” Tatarstan’s president, Rustam Minnikhanov, told reporters standing outside the school following the shooting. He said, a teacher and another woman at the school were also killed.

The seven children killed were eighth-graders. At least 21 people were hospitalized, 18 of them children, and six are in critical condition, according to regional health authorities. Most of the children are between the ages of seven and 15.

Children at the school described to Russian media how they locked themselves in their classrooms on the third floor after hearing explosions and gunfire. In several accounts, students said the gunman tried to breakdown the doors to get to them.

“He sort of started to smash the door,” a pupil, identified as Adelya, told the Russian news site Media.Zona. “Then the police came into the corridor. He ran and started shooting, and a bullet hit our door.”

Authorities have named the attacker as 19 year-old, Ilnaz Galyaviyev, a resident of Kazan and according to local media a former pupil at the school. There were early conflicting reports suggesting two gunmen were present at the attack, but local authorities have since denied that and said he acted alone.

Galyaviyev until last month was a student at a college in Kazan but dropped out in April, the college told the Russian news site, RBC. He graduated from the school four years ago and had been studying programming at the college.

Russian officials have said that Galyaviyev had recently obtained a gun license, receiving one in late April for a semi-automatic shotgun, which was apparently the gun used in the attack.

Russian media have found a channel on the Telegram messenger purportedly created by the alleged shooter a few days before the attack. In photos posted on the channel, a man poses in a long dark coat and a mask with the word “God” in written in Russian on it. In the posts, the alleged gunman refers to himself as “God” and says he will kill a “large number of bio-trash” in the near future.

After police said they had detained the shooter, local media posted a video purporting to show Galyaviyev’s interrogation by police. In the video, a young man, shirtless and tied by his arms and legs to a cage, screams at an officer that “he has realized he’s a God” and that he “hates everyone”.

Although Russia has frequently suffered terrorist attacks, school shootings of the sort seen in the United States are very rare there and this is already one of the most deadly. In 2018, an 18-year-old killed 20 people and injured dozens more at a school in Kerch in Crimea.

President Vladimir Putin expressed condolences to the victims on Monday and immediately ordered authorities to tighten up gun regulations.

Putin’s spokesman Dmitry Peskov said Putin had ordered the head of Russia’s National Guard that oversees gun ownership to develop new rules for the type of weapons civilians are permitted to possess. Peskov said the change was needed to address to assault weapons sometimes being improperly classed as hunting rifles.

Russia’s National Guard quickly said it would fulfil Putin’s order to develop the new rules in coordination with other government bodies.

Following the attack, Tatiana Moskalkova, the country’s ombudswoman for human rights, said she believes the age for gun ownership should be raised to 21 except for those who have served in the armed forces, the state news agency TASS reported.