United Nations Secretary General Antonio Guterres called for $35 billion more, including $15 billion in the next three months, for the World Health Organization's "ACT-Accelerator" programme to support vaccines, treatments and diagnostics against Covid-19.
Some $3 billion has been contributed by countries so far, Guterres told an online event on Thursday, calling it "seed funding".
"But we now need $35 billion more to go from 'start up' to 'scale up and impact'," he said.
"There is real urgency in these numbers. Without an infusion of $15 billion over the next three months, beginning immediately, we will lose the window of opportunity."