The bright flashes were spotted in the early evening in a swathe across the northern half of Spain, from the eastern city of Valencia to the northwestern pilgrimage site of Santiago de Compostela.
In some cases, objects were reported to have fallen to earth.
"I left the house at around 12 minutes to six. I heard a big explosion, like an earth tremor, and a white cloud of smoke formed around a nearby mountain which took a long time to disappear," a local official from the northern region of Palencia told Spanish radio on Sunday.
Civil Guard officials told the radio an object had plunged from the skies in the northern province of Leon.
Spain's civil aviation authority ruled out the possibility of a plane crash.
Jose Angel Docobo, director of the University of Santiago's observatory, said the phenomenon could have been caused by a rock orbiting the sun which had collided with the earth.