Spanish Prime Minister Pedro Sanchez has asked his ministers, public officials and private sector employees to stop wearing ties and stay cool, as heatwaves sweeping parts of Europe stoke demand for energy-guzzling air-conditioning.

"I'd like you all to note that I am not wearing a tie," Mr Sanchez told a news conference.

"This means we can all save from an energy point of view."

High summer temperatures are straining Europe's power systems and raising concern about the prospects for a regional drive to save more gas in case the war in Ukraine prompts further reductions in supplies from Russia.

Striking a more serious note, Mr Sanchez said his government would introduce emergency measures next week to improve efficiency and energy saving.

For now, he said: "I have asked ministers, all public officials, and I would like to ask the private sector too, if they haven't already done so, not to wear a tie when it isn't necessary because that way we will be confronting the energy saving that is so important in our country."

The European Commission released a €210 billion plan aiming to boost renewable energies and reduce energy consumption to put an end to dependency on Russian gas, following Russia's invasion of Ukraine earlier this year.

In response, Spain has adopted several measures including encouraging remote work and the limiting of air conditioning in offices in summer and radiators in winter.

The 27 EU states also agreed on Tuesday "to reduce their gas demand by 15% compared to their average consumption in the past five years, between 1 August 2022 and 31 March 2023, with measures of their own choice," the European Council said in a statement.

It comes as several German cities said this week they would step up efforts to save energy, with Hanover in the north announcing plans to only offer cold showers at public pools and sports centres and Berlin switching off spotlights illuminating its historic monuments.