MIAMI (NYTIMES) - As coronavirus cases surge across much of the United States, leaders are urgently rethinking their strategies to curb the spread, which the nation's top infectious disease expert said on Friday (June 26) were "not working".

For the first time, some governors are backtracking on reopening their states, issuing new restrictions for parts of the economy that had resumed.

Leaders in Texas and Florida abruptly set new restrictions on bars, a reversal that appeared unthinkable just days ago. And Governor Gavin Newsom of California told rural Imperial County, where hospitals have been overwhelmed with patients, that it must reinstate a stay-at-home order, the most restrictive of requirements.

Florida, Utah and South Carolina hit daily highs on Friday for reported new cases, but even leaders outside the new hot zones in the South and West expressed mounting anxiety.

"This is a very dangerous time," Governor Mike DeWine of Ohio said on Friday, as cases trended upward in his state after appearing to be under control for more than a month. "I think what is happening in Texas and Florida and several other states should be a warning to everyone."

The stock market responded badly, with the S&P 500 dropping 2.4 per cent. Losses accelerated after the Texas announcement, adding to investors' concerns that the virus continued to be a threat to the economy.

The shifting assessments of the nation's handling of the virus stretched to the highest levels of the federal government, where Dr Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, made clear that the standard approach to controlling infectious diseases - testing sick people, isolating them and tracing their contacts - was not working.

The failure, he said, was in part because some infected Americans are asymptomatic and unknowingly spreading the virus but also because some people exposed to the virus are reluctant to self-quarantine or have no place to do so.

The renewed sense of urgency comes as the United States confronts a new, treacherous phase of the pandemic, no longer defined by a crisis concentrated in New York City, but by rising cases in many cities and states.

Alabama, Alaska, California, Georgia, Idaho, Missouri, Nevada, Oklahoma and Texas also reported their highest single-day totals of new known cases this week, and the United States set records for daily new cases on both Wednesday and Thursday. By Friday, new daily cases were rising in 29 states.