Almost 836,000 refugees have fled Russia's invasion of Ukraine: United Nations

The number of refugees fleeing the Russian invasion of Ukraine has surged to nearly 836,000, United Nations figures showed Wednesday, as fighting continues to intensify.

In all, 835,928 people have fled across the country's borders, according to the website of UNHCR, the UN refugee agency.

That marks a huge jump from the 677,000 announced Tuesday afternoon by the organisation's chief Filippo Grandi.

More than half have headed west into Poland, according to tallies completed up to Tuesday.

UNHCR figures show that 454,000 people had fled to Poland; 116,000 to Hungary; 67,000 to Slovakia; 65,000 to Moldova, 43,000 to Russia, 38,000 to Romania and 350 to Belarus.

Meanwhile, 52,000 have moved on to other European countries.

An additional 96,000 people had crossed into Russia from the separatist Donetsk and Luhansk regions between February 18 and 23, UNHCR noted.

Russian forces said they had captured the Ukrainian port of Kherson on Wednesday, as Russian and Ukrainian troops battled in the streets of Kharkiv, Ukraine's second-largest city, and President Volodymyr Zelensky said Moscow wanted to "erase" his country.

"The military offensive in Ukraine has caused destruction of civilian infrastructure and civilian casualties and has driven many thousands of people from their homes seeking safety, protection and assistance," UNHCR said.

"There is a clear indication that many more people are on the move. They are in need of protection and support."

UNHCR projects that more than four million Ukrainian refugees may eventually need protection and assistance in neighbouring countries.

The UN on Tuesday launched an emergency appeal for $1.7 billion to provide urgent humanitarian aid to people caught up in the Russian invasion inside Ukraine and for the refugees fleeing the violence.

Grandi said $550.6 million of that was needed to help refugees across the region, with the aim to provide shelter, emergency relief items, cash assistance and psycho-social support.

"We are looking at what could become Europe's largest refugee crisis this century," the refugee agency chief said.

Grandi said the first wave of people fleeing across Ukraine's borders were likely to be people with cars, resources and some connections in other European countries.

But if Russia's military offensive continues and more urban centres are hit, people who are "more vulnerable in every respect" could start to flee, he told reporters.