Boris Johnson has committed £210 million towards a global effort to develop a vaccine for coronavirus.
Downing Street announced the funding this afternoon - making the UK the largest contributor to the international coalition.
Prime Minister Boris Johnson announced the funding during a virtual summit of G20 leaders, Downing Street said.
Mr Johnson said: "While our brilliant doctors and nurses fight coronavirus at home, this record British funding will help to find a vaccine for the entire world. UK medics and researchers are at the forefront of this pioneering work."
He added: "My call to every G20 country and to governments around the world is to step up and help us defeat this virus.
"In the meantime, I want to repeat to everyone that they should stay at home, protect the NHS and save lives."
In a joint statement, leaders of the G20 group - including Prime Minister Boris Johnson - promised a "transparent, robust, co-ordinated, large-scale and science-based global response in the spirit of solidarity".
"Tackling the pandemic and its intertwined health, social and economic impacts is our absolute priority," they said, promising to do "whatever it takes".
The leaders promised to "expand manufacturing capacity to meet the increasing needs for medical supplies and ensure these are made widely available, at an affordable price, on an equitable basis, where they are most needed and as quickly as possible".
They also promised to provide immediate resources to the WHO's Covid-19 solidarity response fund, the Coalition for Epidemic Preparedness and Innovation (CEPI) and Gavi, the vaccine alliance, on a voluntary basis.
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