Dr Joseph Varon, chief of staff at Houston's United Memorial Center, said a surge of infections over the Thanksgiving and Christmas holidays may push hospitals to breaking point.
His comments came as US health officials on Wednesday reported 180,830 new coronavirus cases nationwide – a rise of 2,630 from the previous 24 hours, New York Times data shows.
Just over 100,000 new infections were reported on Thursday, although that figure could be artificially low with fewer people getting tested on Thanksgiving.
Covid-19 deaths have been steadily climbing in recent weeks. Some 2,313 Americans died from the disease on Wednesday, according to the data.
There were 1,178 fatalities reported on Thursday. The total nationwide death toll stands at 263,000.
Dr Varon said he expects hospital admissions to surge over the coming months as the nation waits on a vaccine programme to be rolled out.
"My concerns for the next six to 12 weeks is that if we don't do things right, America is going to see the darkest days in modern American medical history," he told CNN.
"My hospital is full. I just opened two new wings so that I can accommodate for the next few days because I know that a lot of people are going to get sick after Thanksgiving," Dr Varon added.
Where Dr Varon works in Houston, Harris County, 188,000 people have caught the infection – 16,328 of those reported between 12-25 November, according to the New York Times data.
"My nurses in the middle of the day, they will start crying, because they are getting so many patients, and it's a never-ending story," Dr Varon said.
"When they finish finally getting a patient in, they get a phone call from the ER that there is another patient getting admitted."
Coronavirus cases and hospital admissions have been rising right across Texas, but the picture there is similar to large swathes of the country.
As of 26 November 90,481 Americans are hospitalised with Covid-19, according to the New York Times data.
"I worry that the Thanksgiving Day surge will then just add into what will become the Christmas surge, which will then make this one seem as if it wasn't so bad," Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told CNN.
"We have to understand we're in a very dangerous place. People have to stop swapping air," Mr Osterholm added.
“It's just that simple. We are going to see our hospitals literally on the verge of collapse.”
Earlier this week Dr Anthony Fauci, one of the country's leading infectious disease experts, warned the Thanksgiving holidays could act as "surge superimposed on a surge" as he pleaded with Americans to stay home this year.