KIEV - The Russian Investigative Committee has opened a criminal investigation into Wednesday's deadly blast in a college in the city of Kerch in Crimea on charges of a "terrorist act," local media reported.

The unknown explosive device went off in a canteen of the Kerch Polytechnic College, killing 13 people and injuring some 50 others, the committee said in a statement.

Most of the victims are students, it said.

The blast occurred around midday local time (GMT 0900). Social media users said that shooting also occurred at the college.

Crimea was incorporated into Russia in March 2014 following a local referendum. Ukraine says the peninsula was annexed.