VIENNA, Austria (AP) – Winter storms and avalanches across Europe killed at least six people and left three missing, and authorities in Bulgaria declared a state of emergency Friday.

Two men were killed northwest of Frankfurt, Germany, after their car slid out of control on an icy rural road and struck a school bus carrying 45 teenagers, police said. Twenty-three people were injured, two seriously.

In Greece, snowstorms hindered transportation and cut off dozens of villages, and an elderly couple was found dead inside their home in Lamia, 130 miles northwest of Athens.

In Albania, two people were found dead Thursday after an avalanche in the southern village of Zall Dardha. Several villages were isolated by heavy snowfall and attempts to supply them with army and police helicopters have failed because of high winds. The government promised $163,000 in food aid.

The heavy snowfall that pummeled parts of Austria for several days subsided Friday, although experts warned that the avalanche risk remains extremely high in parts of the country. The high risk for snow slides made clearing snow-blocked roads difficult.

Austrian rescue workers said there was little hope that three hunters missing since Thursday in southern Austria’s Styria province were alive.

The workers said the three were buried under a mass of snow brought by an avalanche, but they could not begin digging them out because of the extreme risk of further slides.

The army was using helicopters to evacuate about 500 guests, half of them school children, who had been attending a ski course in a village 115 miles southwest of Vienna that was cut off by several avalanches Thursday.

In Bulgaria, authorities declared a state of emergency Friday for the eastern regions, closing airports after heavy snowfall brought life in the Black Sea city of Varna to a standstill.

Snowdrifts of up to about six feet trapped about 100 vehicles on a road west of Varna.

Blizzards lashed the eastern parts of Bulgaria’s northern neighbor, Romania, causing power outages and forcing road and school closures. The local government in the county of Constanta on the Black Sea coast ordered all traffic suspended after about 150 cars got stuck in snowdrifts.

Heavy snowfall and high winds forced a closure of the airport in Constanta, ports along the Black Sea coast and all schools in Constanta. The main highway linking the capital to the Black Sea also was closed.