Germany has declared an “early warning” of a gas supply emergency, in one of the starkest signs yet that the Russian invasion of Ukraine is spilling over into European energy markets.

The country said that its warning was intended to prepare for the risk of disruption to, or even the end of, natural gas flows from Russia.

Last week, President Vladimir Putin announced that “unfriendly” countries – such as the UK, the US, and the European Union – will soon be required to pay for Russian gas in roubles.

The move is intended to subvert sanctions and shore up Russia’s currency, but has been flatly rejected by the G7 nations, with some like Italy calling it a breach of contract.

The announcement has put European countries like Germany on high alert, however.

German Economy Minister Robert Habeck said on Wednesday that the “early warning” measure was the first of three stages, and did not yet imply a state intervention to ration gas supplies.

But he did urge Germans to reduce consumption, telling a press conference that “every kilowatt hour counts,” according to Reuters.

Russia is estimated to rake in up to $800m every day from its sales of gas to Europe. Germany gets more than half of its natural gas, half of its coal and roughly a third of its oil from Russia.

Mr Habeck added that gas supplies were secure in the short term, and that Germany was keeping an eye on supply flows into the country.

“Nevertheless, we must increase precautionary measures to be prepared for an escalation on the part of Russia,” said Mr Habeck. “With the declaration of the early warning level, a crisis team has convened.”

Klaus Mueller, the head of German network regulator Bundesnetzagentur, said in a tweet that the aim of the early warning was to avoid a deterioration of supply and urged consumers and industry to prepare for “all scenarios”.