“Now the problem is not the money,” he said. “Now we need to get the supplies.”

On Thursday, he was in his basement office, juggling phone calls, social media and email to organize efforts from various donor groups, including the Association of Chinese American Physicians.

Mr. Xu had already secured free shipping through a Chinese airline, he said, and was working on an official channel with the Hubei Province Red Cross to accept and distribute donations of supplies. Struggling to find suppliers, he was brokering deals with factories and importers to secure supplies that had originally been bound for overseas superstores. But resources were still scarce.

“Now China has to borrow from America,” he joked.

On the West Coast, June Liao, the owner of a baby formula export company based in Los Angeles, had amassed 20,000 masks from various sources to donate to Wuhan via the Red Cross. She set up two growing WeChat groups that have collectively raised $48,000 in under 24 hours, she said.

In Washington State, Mr. Shi said he and a handful of others, working as part of a group called the United Chinese Americans of Washington, have established a team to coordinate help. He has ordered 100 masks online. But in the meantime, he has been buying from stores, reading the labels to ensure the masks offer what he deemed to be sufficient protection.

In his WeChat app, he called up a bulletin from officials in Wuhan describing what was needed. While he was not sure if private shipping to China would get through the quarantines, he was hopeful that aid groups would be able to bring in the supplies they are managing to gather.

“In the long run, they will figure out how to supply and deliver to there,” he said. In the meantime, he said, “It’s always good if we can send something to them.”

Angela Chen contributed reporting.