Police say a heavy concrete block thrown from an overhead bridge onto a major highway in Denmark has killed a German woman and seriously injured her husband as their car passed underneath.

Police spokeswoman Charlotte Nyborg says the couple's 5-year-old son was not physically injured in the attack that occurred at 4 a.m. on Sunday morning.

Nyborg said Monday that a 30-kilogram (66 pound) concrete block tile and several rocks were dropped from the bridge for no "known reason" onto the highway near the central city of Odense as the car passed under the bridge. No one else was injured.

Police were investigating the incident as possible murder.

Nyborg said the family was returning to Germany after holidaying in Norway. She declined to identify them or give further details.