At least 10 people have been killed and many more wounded in a bomb explosion at a college in Crimea that one witness told local television also involved an attack by armed gunmen.

The Russian national anti-terrorism committee, a government body, said the explosion at a polytechnic was caused by an “unidentified explosive device”, according to Russia’s Tass state news agency.

The bomb blast took place in the city of Kerch, which is the entry point for a new 19km bridge linking Crimea to mainland Russia.

On local television, the head of the college described an armed rampage with attackers gunning down pupils and teachers, leaving bodies strewn throughout the building. At least one attacker blew himself or herself up, the school director said.

“It was a real terrorist attack, like in Beslan,” the school director, Olga Grebennikova, said, referring to the 2004 terror attack that left more than 330 dead.

Russia’s Investigative Committee declared the assault a terrorist attack and said the explosive device was laced with metal strips that acted as shrapnel when it was detonated

“There are a lot of bodies, a lot of bodies of children,” she said in the video, which was posted to the news site KerchNet. The attackers “ran with automatic rifles, I don’t know what they were, on the second floor, opening offices and killing everyone they could find”.

“I would also be a corpse,” she said. “Because all of my people were shot to death. Kids and employees were killed.”

The committee said early estimates suggested that 10 people had been killed and more than 50 wounded in the explosion, which happened in the college cafeteria.

Reports from witnesses quoted by local media suggested there may have been shooting and an attempt to take hostages prior to the explosion. Police have so far not commented on the incident. Russian media first reported the blast as the result of a gas explosion.

The explosion will attract intense scrutiny from Russian authorities. Crimea was annexed by Russia from Ukraine in 2014, and providing security to the peninsula has been a priority for Moscow.