A former Miss Ukraine on Tuesday called for global support for her country in the face of Russian attacks, highlighting the plight of mothers and children as the world marked International Women's Day.

Veronika Didusenko, who won the beauty queen title in 2018, told reporters in Los Angeles her country was suffering under the onslaught ordered by Russian President Vladimir Putin.

"Right now, millions of Ukrainian children and their mothers are trembling at every sound in the subway stations and bomb shelters," she said.

"Even more heartbreaking is that women are giving birth in such conditions in the shelters."

Tens of thousands of Russian troops have swarmed into Ukraine since the invasion began on February 24, heading towards major cities, including the capital, Kyiv.

More than two million people are known to have fled the country, the bulk of them seeking safety in Poland.

Didusenko said her countrymen would continue to defend their land, but pleaded for help from the outside world, including the imposition of a no-fly zone over Ukraine.

"Ukrainians absolutely have the courage to defend their lands and homes, but in order to stop the endless attacks from the east and north, they are in desperate need of weapons and ammunition. 

"Those remaining in Ukraine need this help the most; those who are under fire from the Russian fascist bombs are begging our allies to close the skies over Ukraine. 

"Unfortunately, their pleas are falling on deaf ears in Washington and Europe."

Didusenko was accompanied by attorney Gloria Allred, who called on US President Joe Biden to allow Ukrainians fleeing the fighting to come to the United States.

"Many of these mothers and children... have no idea where they will be able to live with their children, and if they will be able to return to their former homes," she said.

"As Americans, we must do everything possible to open our doors... to these refugees, and particularly mothers with children. 

"I urge President Biden to immediately announce that he will give Ukrainians the opportunity to come to the United States if they so choose."