The UN refugee agency has said that 1 million people have fled Ukraine since the Russian invasion a week ago. The exodus is without precedent in this century for its speed.
The tally from UNHCR amounts to more than 2 percent of Ukraine's 44 million population on the move in a week.
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The UN agency has predicted that up to 4 million people could eventually leave Ukraine but cautioned that even that projection could be revised upward.
Syria, whose civil war erupted in 2011, currently remains the country with the largest refugee outflows - at more than 5.6 million people, according to UNHCR figures. But even at the swiftest rate of flight by refugees out of Syria, in early 2013, it took at least three months for 1 million refugees to leave that country.
UNHCR spokesperson Shabia Mantoo said on Wednesday that "at this rate" the outflows from Ukraine could make it the source of "the biggest refugee crisis this century."