A winter storm descended on the Balkans Friday, wreaking havoc with traffic and energy supplies while threatening the lives of migrants and people in isolated areas, dpa reported. Daytime temperatures across Bulgaria and the former Yugoslavia are not expected to rise above minus 8 degrees Celsius and may drop to the low 20s below freezing overnight. At the same time, snow was falling heavily in some areas and gale force winds thwarted efforts to clear the roads. Serbia's main highway has been closed in several places because of snow drifts as tall as two metres, state TV RTS reported. Traffic was heavy in spite of the conditions, with Friday the last day before the holiday for Orthodox Christmas. A crash involving 40 vehicles occurred in a blizzard near Nis, 230 kilometres south of the Serbian capital Belgrade. At least 22 people were injured. The weather has aggravated an already difficult situation for more than 1,000 migrants stranded in Belgrade and elsewhere in Serbia without shelter. Around 7,000 others, housed in refugee centres, are also unable to continue toward EU countries because of sealed borders. Road traffic was also disrupted by snow in Bulgaria, Montenegro and Bosnia. In Bulgaria, more than 100 towns and villages were without power as the storm knocked the grid offline, novinte.com reported. Several Montenegrin mountain villages were cut off and without power, while on the Adriatic coast the gale uprooted trees and lifted roofs off buildings. In the port of Bar, local authorities warned people to remain indoors over the coming days. In Croatia, it was the freezing wind which caused the most problems. The gusts, measured at 218 kilometres per hour at one point near Zadar, have cut off many Adriatic islands.