The Black Sea city of Varna was particularly hard-hit yesterday, with cars swept away and streets and houses flooded.
"We can confirm the death of ten people," Varna regional police chief Ivan Kalchev told BTV private television.
The victims included a child, Varna police spokeswoman Ivana Mileva told AFP, adding that "this is probably not the final toll".
Electricity was cut in affected areas and the authorities said it would not be restored for the time being due to safety reasons.
The bad weather is forecasted to continue today.