The United Nations is warning that 265 million people could be pushed to the point of starvation by the end of 2020 with the first increase in global poverty since 1990 unless urgent action is taken.
"My message to the G-20 is step up now or pay the price later. For a relatively modest investment, we can prevent the worst, including the exportation of the worst problems from the most fragile countries," Lowcock told reporters, referencing the group of the world's largest economies.
The U.N. launched its Global Humanitarian Response Plan in March, but has fallen short of its funding goals since then, generating $1.7 billion so far. The initiative targets 63 countries already facing humanitarian crises where COVID-19 and associated lockdowns are just starting to have a profound impact.
"Failure to act now will leave the virus free to circle the globe, undo decades of development and create a generation's worth of tragic and exportable problems," said Lowcock, who serves as the U.N. Under Secretary-General for Humanitarian Affairs.
That staggering figure -- 265 million people on the brink of starvation -- was reached by the U.N.'s Office for the Coordination of Humanitarian Affairs and an Oxford University researcher in the first detailed assessment of its kind.
Lowcock told ABC News he's hoping the U.S. will provide roughly 30% of that $10.3 billion figure. So far, the U.S. has announced $1.5 billion for international assistance, although not all of that has gone to the aid groups and international agencies Lowcock is raising funds for.
Despite the worsening outbreak in America, which is already leading the world in COVID-19 deaths and cases, Lowcock told ABC News the U.S. "remains the indispensable nation."
"[It's] only when there is U.S. leadership and mobilization of others that there's a really effective global response," he said, adding a warning, "Nobody, including no one in the U.S., will be safe from this virus until everybody's safe from it."
But with shortages of personal protective equipment and insufficient testing, some have said the U.S. needs to focus on its own outbreak.
So far, only 0.1% of all U.S. emergency funding has gone to international assistance, but now there is growing momentum in Congress to do more.
A bipartisan group of senators wrote to Majority Leader Mitch McConnell, R-Ky., and Minority Leader Chuck Schumer, D-N.Y., urging them to prioritize "significant U.S. investment in the international response" in the next emergency funding package. In the House, at least 125 members have signed on to a similar letter to House leadership, warning, "We cannot afford to under-resource global foreign assistance as it is an essential component of a COVID-19 response."
While more U.S. assistance may help mitigate the effects worldwide, Lowcock said the world's richest economies were slow to act and "waited too long to grip this."
In unusually critical tones, Lowcock has pleaded for greater assistance.
"I don't have a magic money tree," he told reporters Thursday, "but the donors do and they've used it to protect, I think wisely, their own economies and their own countries, and what I'm saying is it would be a very good idea to use just 1% of that money in your own interests as well as an act of human empathy and generosity to protect the poorer countries."
In particular, the World Food Program warned earlier this week that 10 countries already face deep food crises -- Yemen, the Democratic Republic of the Congo, Afghanistan, Venezuela, Ethiopia, South Sudan, Syria, the Sudan, Nigeria and Haiti -- totaling 135 million people.
But that could almost double to 265 million people if this urgent appeal isn't met, the agency estimated.
Over 588,000 people have died globally from the coronavirus, which has infected 13.6 million people in 216 countries, areas or territories.