Connecticut's Governor Ned Lamont said the six-week-old baby was "one of the youngest lives lost anywhere due to complications relating to COVID-19".
Confirmed coronavirus infections around the world are approaching one million, as a six-week-old baby in the United States became the youngest known victim of the disease.
Half the planet is under some form of lockdown as governments struggle to tamp down a virus that has killed tens of thousands of people.
Those restrictions - while necessary for health - risk causing global food shortages, experts warn, as supply chains gum up and panic buying sparks export controls.
The death toll from COVID-19 has continued its relentless march upwards, with more than 46,000 people known to have died worldwide.
The United States, which now accounts for almost a quarter of reported global infections, logged its 5,000th death, according to a tally by Johns Hopkins University.
And President Donald Trump said things were going to get worse.
"We're going to have a couple of weeks, starting pretty much now, but especially a few days from now, that are going to be horrific," he said.
"But even in the most challenging of times, Americans do not despair. We do not give in to fear."
Among the latest US fatalities was a six-week-old baby who was taken to a Connecticut hospital late last week.
"Testing confirmed last night that the newborn was COVID-19 positive," the state's Governor Ned Lamont tweeted. "This is absolutely heartbreaking."
He said the newborn baby was brought to the hospital unresponsive and could not be revived.
"We believe this is one of the youngest lives lost anywhere due to complications relating to COVID-19," he said.
"This is a virus that attacks our most fragile without mercy."
The novel coronavirus has chiefly affected the elderly and those with pre-existing medical conditions, but a number of recent cases have highlighted that it can affect people from all walks of life.
The dead have included a 16-year-old in France, a 12-year-old in Belgium and Ismail Mohamed Abdullah, 13, in Britain, whose family said the "gentle and kind" boy had no underlying health issues.
World Health Organization head Tedros Adhanom Ghebreyesus said the disease's rapid spread was alarming.
"Over the past five weeks, we have witnessed a near exponential growth in the number of new cases, reaching almost every country," he said.
"The number of deaths has more than doubled in the past week. In the next few days, we will reach one million confirmed cases and 50,000 deaths."
People in Australia must stay at least 1.5 metres away from others and gatherings are limited to two people unless you are with your family or household.
If you believe you may have contracted the virus, call your doctor (don’t visit) or contact the national Coronavirus Health Information Hotline on 1800 020 080. If you are struggling to breathe or experiencing a medical emergency, call 000.
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