20 Million Miles To Earth (1957 Classic SciFi -COLOR-)

http://www.imdb.com/title/tt0050084/

When the first manned flight to Venus returns to Earth, the rocket crash-lands in the Mediterranean near a small Italian fishing village. The locals manage to save one of the astronauts Colonel Calder, the mission commander. A young boy also recovers what turns out to be a specimen of an alien creature. Growing at a fantastic rate, it manages to escape and eventually threatens the city of Rome forcing the military to take drastic action.