The Mysterians

A harvest celebration party is disturbed by unusual natural events and by a gigantic monster which rises from behind the hills. The steel creature begins to destroy everything on its path, obliterating roads and bridges as he heads toward the city. Conventional weapons have no effect on the monster and its destructive rays.

It turns out that the monster is remote-controlled. Astronomers later uncover an imminent alien invasion from the star of Mysterians...