The European Commission on Wednesday set out its proposal for EU member states to let Ukrainians fleeing Russia's invasion stay and work in the bloc for an initial two years. 

The urgent plan is being rolled out as over 650,000 people have already fled across the border into eastern EU states Poland, Slovakia, Hungary and Romania that neighbour Ukraine. 

Many more are expected as the Kremlin's forces unleash ferocious bombardments against major cities.

The United Nation's refugee agency, UNHCR, said on Tuesday an estimated one million people were displaced inside Ukraine by the Russian invasion.

"Europe stands by those in need of protection. All those fleeing Putin's bombs are welcome in Europe," European Commission chief Ursula von der Leyen said in a statement. 

"We will provide protection to those seeking shelter and we will help those looking for a safe way home."

The proposal by the EU's executive would give refugees from Ukraine and family members a residence permit and the right to access work and education for an initial two years.

The Commission said it would be able at any time to ask member states to extend the protections by one more year or end them if the situation stabilises in Ukraine.  

The plan is to be put to EU interior ministers meeting Thursday and has to be agreed by a majority of at least 15 member states. 

European capitals have already expressed broad support for the move as they scramble to cope with the fallout from Russian President Vladimir Putin's invasion.  

If approved it would be the first time the bloc would be activating its 2001 Temporary Protection Directive. 

The directive was originally drawn up for refugees from the conflicts that wracked the former Yugoslavia, with provisions for handling a massive inflow of people and measures to distribute them across EU nations. But it has never been used until now.

The EU said the proposal would also cover "non-Ukrainian nationals and stateless people legally residing in Ukraine" such as asylum-seekers.

The Commission's proposal also includes temporarily relaxing border controls to allow people from Ukraine to enter the EU even if they do not have a valid passport or visa.  

Under existing rules Ukrainians with passports bearing biometric data are allowed to enter the EU without a visa and stay for up to three months.