All Russian gas supplies via Ukraine to Bulgaria, Turkey, Greece and Macedonia were halted on Tuesday as a result of the Moscow-Kiev price row, Bulgaria's economy ministry said.
"As of 3.30 a.m. (0130 GMT) supplies ... to Bulgaria as well as the transit to Turkey, Greece and Macedonia have been suspended," the ministry said in a statement. "We are in a crisis situation."
Bulgaria, which relies almost entirely on Russian gas for its needs, will be worst hit as, like Macedonia, it has no access to alternative pipeline routes, reported Reuters.
The ministry told industrial users to switch to alternative fuels such as oil and urged households to start using other means for heating rather than central heating that runs on gas.
Prime Minister Sergei Stanishev called an emergency meeting later on Tuesday to discuss the situation.
Bulgaria, where temperatures dropped below minus 15 degrees overnight, started pumping a maximum 4.3 million cubic metres of gas from its sole gas storage facility, the ministry said.
The country currently consumes about 11 million cubic metres of gas a day.
Turkey can also receive Russian gas via a pipeline under the Black Sea and Greece gets additional supplies from Ankara.