People who are settled in the UK will be able to bring their Ukrainian immediate family members to join them, the prime minister has announced.
Boris Johnson said the UK would not “turn our backs in Ukraine’s hour of need”.
Speaking to the congregation at the Catholic Cathedral of the Holy Family in London’s Mayfair, he said he had never seen “so clear a distinction between good and evil” as the conflict in Ukraine.
He later announced a further £40m of humanitarian aid for the country.
The government has been facing growing calls to waive visa rules for Ukrainians seeking sanctuary in the UK amid the ongoing Russian invasion.
Before the latest announcement, only those Ukrainians who were deemed to be “dependants” of those already in the UK were being guaranteed entry.
And European Union member states have supported plans to take in all Ukrainian refugees for up to three years, with no need for them to apply for asylum.
Downing Street said the change in UK policy would “benefit many thousands of people who at this moment are making desperate choices about their future”.
Speaking to the media, Mr Johnson said: “We want to be as generous as we possibly can, and certainly we want people who have relatives in Ukraine to be able to bring them over as fast as possible.
“We want to make sure that we have routes for people fleeing disaster, war, persecution in Ukraine to come here.”
That statement came separately from his visit to the Cathedral, where he told the congregation that the UK would do “everything it can to help economically, politically, diplomatically, militarily”.
He said the people of Ukraine were facing “the darkest times in modern memory” and described Russia’s invasion as a “barbaric and unprovoked attack”.
Mr Johnson told the congregation that Ukrainians were neighbours with the UK, through shared ideals, as well as literally – with hundreds of thousands having come to live and work in Britain over the decades.
“I’m going to stress that there is no hostility in my heart towards the Russian people, none whatever – quite the reverse,” he said.