The body of a 58-year-old woman was found buried under mud in her home after her husband, who arrived from Russia, reported her missing, officers said.

Three people were previously reported killed in the storms that lashed Elenite, a resort town on the edge of the Black Sea, on Friday.

"Among the victims were two rescuers, one a border police officer and the other a tractor driver," Interior Minister Daniel Mitov told Bulgarian state radio.

Another person was caught by the rising waters at a hotel, the authorities said.

Videos shared on social media showed torrents of muddy water washing away cars in one of the main streets in Elenite.

The flood, which occurred shortly before midday on Friday, damaged buildings and roads.

A state of emergency was declared in several communities in the southeast and northwest of Bulgaria.

Environmentalists have warned for years about over-development on the Black Sea coast, arguing that it worsens damage during natural disasters.