Greeks voiced despair and disbelief on Thursday after a flash flood killed at least 15 people and left hundreds homeless, with many blaming a system that allowed houses to be built on dried up river beds.

In the towns of Nea Peramos and Mandra west of Athens, crumpled cars and mangled furniture lay on roads and inside homes caked in the thick mud left behind by a raging torrent that smashed through homes.

Residents wept and voiced anger as they salvaged through their belongings and cleaned up the damage.

Bad weather continued on Thursday and officials said they were waiting for conditions to improve before giving a clearer picture of the damage. Five people were still missing.

Experts blamed haphazard construction. Both towns were built along an old motorway linking Athens to the Peloponnese city of Corinth. As building crept closer to the road, streams that would have drained runoff from the nearby Pateras mountains were blocked.