Vienna -- Eastern Europe took crisis measures in response to a complete cut in supplies of Russian gas on Wednesday, switching off heating in public transport, closing schools and curbing use by big industries.

As most of Europe shivered in freezing conditions -- temperatures measured minus 20 degrees Celsius (minus four degrees Fahrenheit) in some parts -- Austria, Slovenia, Czech Republic, Slovakia and Romania reported a total halt in Russian gas supplies for the first time.

Bulgaria, Hungary, Croatia and Bosnia experienced a second day of complete stoppage following the Russia-Ukraine dispute over gas prices.

While many remained confident their reserves would compensate for the Russian gas shortage for at least a few weeks, others had to resort to drastic measures.

Slovakia and Romania have declared energy emergencies.

Two fertilizer plants in Bulgaria, Neochim and Agropolychim, and many glass and metal-working plants, bread producers and breweries have halted production or face closure owing to the gas shortage.

In Hungary, the Japanese car manufacturer Suzuki announced it would close down until Monday.

In Sofia, mayor Boiko Borisov ordered heating in all public transportation to be switched off and buses running on gas were temporarily withdrawn from use.

Drivers of gas-powered taxis, which make up 50 percent of the capital's cabs, threatened to strike as they found gas stations closed.

Education Minister Daniel Valchev also ordered schools to be closed if temperatures dropped below 18 degrees Celsius in classrooms.

Eighty schools across the country asked to be closed, the ministry of education said.

The gas shortage in Bulgaria, which depends for 92 percent of its consumption on Russian gas, already led to a heating stoppage in the towns of Varna, Bourgas and Razgrada.

In Hungary, Croatia and Bulgaria, gas deliveries to major industries were reduced to guarantee supplies for households, schools and hospitals.

In Austria, large-scale industrial users agreed to coordinate gas usage among themselves and gas-fired power plants would switch to oil and coal.

"Austria must prepare itself for an extended halt in gas supplies," warned Economy Minister Reinhold Mitterlehner.

In Slovakia, Prime Minister Robert Fico said that his government might reopen a power generating unit at Jaslovske Bohunice nuclear plant if the freeze of gas supplies from Russia continued.

Bulgaria's President Georgy Parvanov mooted a similar idea the day before for one of its nuclear reactors in Kozloduy, which the EU ordered Sofia to shut down in 2007 over safety concerns.

Hungary and Romania called on plants and factories to switch over to alternative fuels, if they could.

This was the case at Budapest's Ferihegy international airport, which switched its heating system to oil, as did a heating plant in the Slovenian capital Ljubljana and part of the power grid in Austria.

The Bosnian city of Sarajevo, where the majority of households rely on gas heating, was turning to alternative energy sources but only had enough reserves for another seven days, city officials warned.

In Bulgaria, major gas provider Overgas and the state-owned gas monopoly Bulgargaz halted all deliveries to major industrial customers except those that could not switch to alternative fuel.

Sofia also turned off facade lighting on public buildings to save electricity, as distribution companies warned of possible power outages after many people switched to electricity for heating.

Countries such as Hungary, Croatia, Austria and Romania said however that they could continue to rely on some domestic production, while Czech Republic noted it was still receiving gas from Russian and Norwegian sources via Germany.

Hungary has three billion cubic meters of gas in reserve, Austria 1.7 billion, Romania 2.2 billion. These stocks were estimated to be sufficient to provide for households through the winter.

In Bulgaria, 570 million cubic meters of gas in reserve could last for anything between one and three months.

Slovenia, whose gas consumption only makes up about 14 percent of total energy consumption, appealed to people to limit gas usage but had not taken any further measures to tackle the drop.

Russia, the world's biggest natural gas supplier, has halted gas supplies for European customers via Ukraine, following a gas dispute between the two neighbors which trade blame over the causes of the cuts now hitting customers in third countries.

Sim Sim Wissgott/AFP/Expatica