The United States recorded its first coronavirus fatality on Feb. 29. It took 38 days to reach 10,000 deaths and just nine more days to go from 10,000 fatalities to 30,000. The previous high single-day death toll was 2,364 on Tuesday.
US confirmed cases topped 635,000 in the United States and 2 million globally.
Despite the spike in deaths, there were tentative signs in some parts of the country that the outbreak was beginning to ebb.
Governors of about 20 states with few coronavirus cases believe they may be ready to start the process of reopening their economies by President Donald Trump's May 1 target date, a top US health official said on Wednesday.
Governors in harder-hit states - New York, California, Louisiana, New Jersey, Massachusetts and Michigan - said there was a need for more widespread testing before starting to end the coronavirus shutdown, which has thrown millions out of work with the closing of restaurants, businesses and schools.
Health officials have noted that death figures are a lagging indicator of the outbreak, coming after the most severely ill patients fall sick, and do not mean stay-at-home restrictions are failing to curb transmissions.
New York state and some other hard-hit areas continue to report sharp decreases in hospitalizations and numbers of patients on ventilators, although front-line healthcare workers and resources remained under extraordinary stress.
Officials have also cautioned that coronavirus-related death figures are likely an undercount due to people dying at home or in nursing homes who were never tested for the virus.