An appeal is being launched by the UK's Disasters Emergency Committee to help the hundreds of thousands of Ukrainians fleeing the conflict.
Fifteen UK aid agencies - including the British Red Cross, Oxfam and Save the Children - are joining together to ask the public to donate.
The DEC has thanked the Queen for making a "generous" private donation.
Homes in Ukraine have been destroyed and water supplies, hospitals and schools have been hit, the DEC says.
The charities say people urgently need food, water, shelter and medical care.
The appeal will help people who have fled Ukraine, but also those who have been displaced to other parts of the country.
All public donations will be doubled by the UK government, up to a total of £20m.
More than one million people have left Ukraine since the war began last Thursday, according to UN estimates - most heading to Poland and other neighbouring countries. The EU has warned up to four million Ukrainians may eventually be forced to flee.
Despite EU nations waiving requirements for travel documentation, many people have faced waits of several days at the border in freezing temperatures, in queues up to 10 miles (15km) long.
'Lost and scared'
The DEC said the majority crossing the borders are women and children, arriving with only what they can carry.
Andrew Morley, president and chief executive of the charity World Vision, said after visiting relief operations at Ukraine's border with Romania and Moldova that he had "never seen a more heartbreaking situation".
"All of the children I met were crossing the border in tears, with pain and fear in their eyes. They were lost and scared. They need the basics - simple, practical help," he said.
DEC chief executive Saleh Saeed added: "I could never have envisaged launching a humanitarian appeal in Europe in 2022. But tragically, that's exactly where we find ourselves."
He said charities were working to reach people in Ukraine quickly, "as the brutal conflict turns lives upside down".
"Families, including many children, have been forced to leave everything they know behind to find safety and desperately need food, water and shelter," he said.
Speaking later to the BBC, Mr Saeed praised the UK public for the support already offered to Ukraine and said cash donations were currently the best way of helping.
Food and aid materials were available in Ukraine, he said, adding that donating money was the "quickest and most effective way" of getting help to people.
Reflecting on the UN's latest estimate of refugee numbers, he added: "Today, sadly, that one million figure has been crossed. One million people who have fled Ukraine across into neighbouring countries, leaving behind their homes."
The appeal will be broadcast on all BBC TV and radio stations, ITV, Channel 4, Channel 5 and Sky on Thursday.
DEC members and local aid agencies working with them say they are operating in Ukraine and in the neighbouring countries of Poland, Romania, Hungary, Moldova and Slovakia.
They are using donations to provide trauma care along with medical treatment, food, water and shelter.
What is the DEC?
- The committee brings together 15 leading UK aid charities to provide and deliver aid to ensure successful appeals
- The charities include Oxfam, Save the Children UK, Age International, British Red Cross, Cafod, Christian Aid and Islamic Relief
- Its website provides more details of its current appeals