More than one million civilians have fled Ukraine because of the Russian invasion, according to the United Nations (UN).
The European Union (EU) says up to four million people may try to leave and that it will welcome refugees with "open arms".
Which countries are Ukraine's refugees fleeing to?
Refugees are crossing to neighbouring countries to the west, such as Poland, Romania, Slovakia, Hungary and Moldova. Smaller numbers have gone to Russia and Belarus.
What help are countries providing?
In Poland and other countries bordering Ukraine, refugees can stay in reception centres if they do not have friends or relatives to stay with. They are given food and medical care.
Poland is also preparing a medical train to transport wounded Ukrainians.
Hungary and Romania are offering cash allowances for food and clothing. Children are being given places in local schools.
The Czech Republic will allow refugees to apply for a special type of visa in order to remain.
Poland and Slovakia have asked the EU for help providing for refugees. As a result, Greece and Germany are sending tents, blankets and masks to Slovakia, while France is sending medicine and other medical equipment to Poland.
The EU is preparing to grant Ukrainians who flee the war a blanket right to stay and work throughout the 27 nations for up to three years.
They would also receive social welfare and access to housing, medical treatment and schooling for children.