People wait in a parking lot to help refugees arriving from Ukraine with transportation and accommodation to different cities in Poland and other countries after Russia launched a massive military operation against Ukraine, in Przemysl, Poland February 26
People wait in a parking lot to help refugees arriving from Ukraine with transportation and accommodation to different cities in Poland and other countries after Russia launched a massive military operation against Ukraine, in Przemysl, Poland February 26, 2022. Reuters / KACPER PEMPEL

The European Union needs to prepare for millions of Ukrainian refugees arriving in the bloc, EU Home Affairs Commissioner Ylva Johansson said on Sunday, as Russian President Vladimir Putin ordered his nuclear-armed forces to be put on high alert.

Thousands of Ukrainian civilians, mainly women and children, have fled into neighbouring countries since Russia's invasion, the biggest assault on a European state since World War Two, began last Thursday.

At least 300,000 refugees had already arrived in the EU by Sunday and many more were likely to come, Johansson said.

"I think we need to prepare for millions," she told reporters in Brussels, where the bloc's home affairs ministers gathered for a special meeting to discuss the fallout of the war in Ukraine.

Denmark said it was ready to take in Ukrainian refugees.

"I have signalled very clearly that the Danish door is open and that we are willing to help," Immigration Minister Mattias Tesfaye said.

Germany warned against putting up bureaucratic hurdles, while France said EU countries will consider "in the next hours and days" if they need to put in place a resettlement programme for Ukrainians fleeing the conflict.

Johansson praised European citizens for their solidarity and hospitality in the crisis.

"I am proud of how the European citizens at the borders are showing concrete solidarity with Ukrainians fleeing this terrible, aggressive war," she said.