Arizona has become the most closely watched state in the United States by health officials who are expressing alarm that a second wave of the coronavirus may be taking hold in the state and possibly elsewhere as nearly half the states report a sudden spike in cases.

Eleven Arizona hospitals have hit ICU (intensive care unit) capacity, according to Ann-Marie Alameddin, the president of the Arizona Hospital and Healthcare Association.

With hospitalizations spiking rapidly, Arizona lawmakers and medical professionals are warning there might not be enough emergency room beds to handle what could be a big influx of new cases. More than 1,500 new cases were reported along, with 25 deaths in the past 24 hours, officials said on Wednesday.

Arizona's largest hospital system warned over the past week that its intensive care units are filling up and ventilator use was on the rise. The state's top health official has asked hospitals to activate their emergency plans for increasing their bed capacities.

Senate Minority Leader Chuck Schumer, Democrat from New York, on Thursday asked for members of the Trump administration's Coronavirus Task Force, specifically Dr Anthony Fauci and Dr Deborah Birx, to conduct a briefing for Democratic senators next week on the spike in cases in Arizona and elsewhere across the US, according to his office. 

Cases are rising in nearly half the states, according to an Associated Press analysis. Texas has more hospitalized COVID-19 patients than at any previous time. The governor of North Carolina said recent jumps have caused him to rethink plans to reopen schools or businesses.

Houston-area officials said they are "getting close" to reimposing stay-at-home orders and are prepared to reopen a COVID-19 hospital established but never used at a football stadium, as virus cases expand in the fourth-largest US city, Bloomberg News reported.

The announcement by Harris County Judge Lina Hidalgo and Houston Mayor Sylvester Turner on Thursday came a day after the Lone Star state recorded its highest one-day tally of new cases since the pandemic emerged.

"We may be approaching the precipice of a disaster," said Hidalgo, the highest-ranking county executive. "It's out of hand right now. The good news is it's not severe out of hand."

As the pandemic has been pushed to the sidelines by the nationwide focus on race relations, the number of infections in the US has reached more than 2 million. 

More than 27,000 new cases and almost 1,000 deaths were reported on Wednesday alone, according to Johns Hopkins University. More than 113,000 Americans have died since the virus emerged here a few months ago.

Dr Ashish Jha, director of the Harvard Global Health Institute, said the US must be prepared for 100,000 victims in the next few months.

"The pandemic is still here. Between 800 and 1,000 people are dying a day," Jha tweeted. "We can't become immune to this. We can't."

Experts aren't sure why states are experiencing an unexpected uptick in cases, but that the lifting of lockdown restrictions, isolated outbreaks and the virus catching up to communities previously not affected may each play a role. 

"This virus is much more spotty," said Arnold Monto, professor of epidemiology at the University of Michigan School for Public Health. "It is so complicated that when people give you a simple answer to this, it's probably not right."

In Arizona, public health experts in the state have blamed the relaxing of social distancing for the spread, The Arizona Republic reported. Arizona began to reopen gyms, restaurants and other businesses in mid-May. The state hasn't required all individuals to wear masks in public, but workers who interact with the public are expected to have a mask.

While Governor Doug Ducey has insisted this "is not a crisis situation" and suggested the rise in the number of cases is due to an increase in testing, critics have accused the Republican governor of setting a bad example by not wearing a mask while in public.

They say that Arizona residents, who initially took the coronavirus threat seriously, have grown lax about social distancing and face coverings, and that the result is a rise in new cases. 

"Arizona is not ready for this," said state Representative Kelli Butler, the Democrats' ranking member of the state's House Health Committee. "Our hospitals are sounding the alarm. We're hearing that the hospitals lack the ICU capacity needed to deal with this, and key equipment needed to treat people."

Marcy Flanagan, director of the Maricopa County Department of Public Health, echoed Butler's concern during a news conference last week.

"We're starting to see some indicators that the number of COVID-19 cases is increasing in Maricopa County, and we have enough information to know these increases are not due to just an increase in testing that is occurring," said Flanagan, whose county includes Phoenix, the fifth-most populous city in the country.

While the number of daily tests has increased from 4,200 to 7,900 over the past two weeks, the rate at which those tests are coming back positive is also increasing. Experts said such a trend suggests the virus is actually spreading, not just that more tests happen to be finding more cases.

Dr Kacey Ernst, an infectious disease epidemiologist at the University of Arizona, said all signs seem to point to increasing transmission of the disease. Increased testing could explain the rise in cases, but not increased hospitalizations, she said. Arizona does appear to be increasing more than other states, she said.

Health experts have taken notice of Arizona's trajectory and said it could need another stay-at-home order to curb the spread.

"There are three state warnings worth issuing today for COVID, Andy Slavitt, a former administrator of the Centers for Medicare and Medicaid Services under President Barack Obama, tweeted Tuesday. "Not panic, but time to consider actions." Arizona was on the list, along with Arkansas and Utah. 

"I would go so far as to say alarming," said Dr William Hanage, an epidemiology professor at Harvard University's T.H. Chan School of Public Health. "The only sort of crumb of comfort that I can find is that I think, in general, it's sort of easier to social distance in Arizona than it is in some places.''