At least 57 people have been killed by Russian airstrikes and shelling, Ukrainian authorities said Thursday.

Ukraine's Health Minister Oleh Lyashko said 169 more were wounded.

Russia launched a full-scale invasion of Ukraine on Thursday, unleashing airstrikes on cities and military bases and sending troops and tanks from multiple directions in a move that could rewrite the world's geopolitical landscape.

Ukraine’s government pleaded for help as civilians piled into trains and cars to flee.

Lyashko also said Thursday that Ukraine’s authorities are repurposing the country’s health care facilities to make room for those who need medical assistance because of the hostilities.

Separately, the U.N. refugee agency said around 100,000 people have fled their homes within Ukraine and several thousand more have left the country since the invasion started.

"We believe that some 100,000 people must have already left their homes and may be displaced inside the country, and several thousand have crossed international borders," United Nations High Commissioner for Refugees (UNHCR) spokesperson Shabia Mantoo told the Agence France-Presse (AFP).

UNHCR Filippo Grandi had voiced serious concern at the rapid deterioration of the situation as military operations unfolded across Ukraine and urged neighboring countries to keep their borders open for those seeking safety and shelter.

"We are continuing to closely follow the situation and are reinforcing our operations in Ukraine and neighboring countries," the agency said.