Twenty people were killed by a gunman at a college in the Black Sea region of Crimea who set off a bomb in the cafeteria and went through the building shooting anyone he saw.
Law enforcement officials said they were treating the incident as a terror attack. Video footage from the scene showed armored personnel carriers and military trucks lined up on the approach to the college, in the Crimean city of Kerch.
A local resident said officials had instructed parents to collect their children from schools and kindergartens in the city for their safety.
Olga Grebennikova, the college's director, told Crimean media outlets in an interview outside the college that the bodies of children were everywhere.
The Investigative Committee, the law enforcement body that investigates major crimes, said initial information was that an explosive device packed with metal objects had gone off in the cafeteria of the college.
An employee at a hospital in Kerch was quoted as saying that 18 people had already been admitted with injuries from the explosion, and that doctors were expecting around 50 more wounded people to be brought in.
"There are already lots of people in the emergency room, and in the operating theatre," the TASS news agency quoted the employee as saying.
Photographs from the scene of the blast posted by local media outlet Kerch.FM showed that the ground floor windows of the two-story building had been blown out, and that debris from the building was lying on the floor outside.
Ambulances and fire fighters were at the scene. One person could be seen on a stretcher being carried onto a bus.
The technical college provides vocational training to teenage pupils.
Russia annexed Ukraine's Crimea region in 2014, prompting international condemnation and Western sanctions. Kerch is the point on the peninsula where a bridge linking Crimea to Russia makes landfall on the Crimean side.
Russian President Vladimir Putin opened the bridge to road traffic in May this year, getting behind the wheel of a truck to drive it across the bridge.
Reuters contributed reporting.