A gunman has launched an attack on a school in the Russian city of Kazan that left at least nine people dead - including seven youngsters - and sent students running out of the building as smoke poured from one of the windows.
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At least 21 others were hospitalised, six in extremely grave condition, authorities said.
The attacker, identified only as a 19-year-old, was arrested, officials said.
They gave no immediate details on a motive.
But Russian media said the gunman was a former student at the school who called himself "a god" on his account on the messaging app Telegram and promised to "kill a large amount of biomass" on the morning of the shooting.
Attacks on schools are rare in Russia, and President Vladimir Putin reacted by ordering the head of the country's National Guard to revise regulations on the types of weapons allowed for civilian use.
Four boys and three girls, all eighth-graders, died as well as a teacher and another school employee, Tatarstan Republic Governor Rustam Minnikhanov said.
Footage released by Russian media showed students dressed in black and white running out of the building.
Another video depicted shattered windows, a stream of smoke coming out of one, and the sound of gunfire.
Dozens of ambulances lined up at the entrance.
Russian media said while some students were able to escape, others were trapped inside during the ordeal.
"The terrorist has been arrested, 19 years old. A firearm is registered in his name. Other accomplices haven't been established. An investigation is underway," Minnikhanov said.
Authorities said the 21 hospitalised included 18 children.
Authorities announced a day of mourning on Wednesday and cancelled all classes in Kazan schools.
Authorities tightened security at all schools in the city of about 1.2 million people, 700km east of Moscow.
Russian lawmaker Alexander Khinshtein said on Telegram that the suspect in the Kazan attack received a permit for a shotgun less than two weeks ago and that the school had no security aside from a panic button.
Authorities in Tatarstan ordered checks on all gun owners in the region.
Putin extended condolences to the families of the victims and ordered the government to give them all necessary assistance.
Russian officials promised to pay families 1 million roubles ($A17,210) each and give 200,000 to 400,000 roubles to the wounded.
The Kremlin sent a plane with doctors and medical equipment to Kazan and the country's health and education ministers headed to the region.
Australian Associated Press
