Eighteen people were killed when gunmen burst into a college in the Black Sea region of Crimea, set off a bomb in the cafeteria, and went through the building shooting anyone they saw, officials and the college's director said on Wednesday.

Law enforcement officials said they were treating the incident as a terror attack. Video footage from the scene showed armoured personnel carriers and military tucks 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.

It said in a statement that 19 people had been killed and around 50 wounded, many of whom were teenage children.

Russia annexed the Black Sea peninsula of Crimea from Ukraine four years ago, prompting international condemnation and Western sanctions.

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-storey building had been blown out, and that debris was lying on the floor outside.