Sofia/Belgrade - Strong winds hitting the northern Balkans blew rooftops off of buildings and triggered a state of emergency in one Bulgarian municipality, local reports said Wednesday.

The Zavet municipality, some 350 kilometres north-west of the capital Sofia, was hit late Tuesday by what local reports described as a tornado. It tore the roofs of 250 homes in the area and knocked trees down.

A state of emergency was declared in the area, as teams rushed to clear tree trunks from the roads and restore the power supply. No injuries were reported and damage was still being assessed Wednesday.

Across the border to the west, in Serbian capital Belgrade, the storm knocked down several trees and a large fence, and also tore away a 10-metre helium-filled balloon from a downtown square and drove it across the Danube River, 40 kilometres to the east.

The balloon, continents superimposed on the map of Belgrade, was put up in celebration of Planet Earth Day. Deflated, it was returned for repair and would be suspended again for the Eurosong contest in the latter half of May. (dpa)