Three people died Monday when two small planes collided over the airport in the northern Spanish city of Castrillon, authorities said.

First responders found the bodies of three of the four people who were aboard the two aircraft and were continuing to search for the fourth person.

One of the planes went down in an airport parking lot, while the other came to rest on a nearby hilltop.

The planes were part of a three-aircraft caravan that took off from San Sebastian, in Spain's Basque region, bound for Vilar de Luz, Portugal.

The third airplane landed safely at the airport in Santander.

Though the cause of the collision remains unknown, authorities noted that Castrillon was experiencing fog and heavy rain at the time of the accident.