Saying they fear the state is on the cusp of a second wave of coronavirus infections, New Jersey officials sounded their loudest alarms since spring’s end, while Pennsylvania Gov. Tom Wolf said he was “very concerned” about the virus' new trajectory in the commonwealth.

“This wave has the potential to become a surge,” said New Jersey Health Commissioner Judith Persichilli, if residents do not keep taking preventive measures such as masking, social distancing, and washing hands.

The high number of people testing positive comes after several days of rising cases in the two states and as the United States averages about 5% more new cases this week than last. The increases here and elsewhere also come amid renewed focus on the coronavirus in the presidential campaign due to President Donald Trump’s infection.

Democratic nominee Joe Biden will appear at a moderated town hall in Philadelphia on Oct. 15, the day the second presidential debate was to take place, his campaign and ABC News announced Thursday, after Trump, who has COVID-19, rejected a proposal to conduct the debate virtually.

The town hall, which will be moderated by anchor George Stephanopoulos, was booked after a day of back-and-forth between the campaigns about how and when the scheduled two remaining debates should be held. Biden’s campaign said Thursday he had tested negative for the virus for the fifth time since Trump was diagnosed.

Pennsylvania reported 1,376 new coronavirus cases Thursday, while New Jersey — which had been reporting lower daily numbers than Pennsylvania for months — reported 1,301, more than double its case reports in preceding days.

It was the highest number of cases reported in one day since early May for Pennsylvania and late May for New Jersey, surpassing already high numbers from earlier in the week.

Philadelphia reported 225 new cases, also reflecting the rising trend, as SEPTA officials unveiled a Suburban Station mural dedicated to their frontline workers just two days after telling employees another worker had died of the virus — bus operator Mbassa Bessike became the transit authority’s eighth employee to die of COVID-19, according to a letter to employees obtained by The Inquirer on Thursday.

The United States has recorded more than 7.5 million cases and more than 212,000 deaths since the pandemic began. Case increases are hitting the Upper Midwest hard, with North Dakota reporting more than 555 daily cases per million population, breaking the pandemic record set by Florida in mid-July, according to Johns Hopkins University data.

In recent days, California and Texas have surpassed New Jersey in confirmed deaths, making New Jersey’s death toll of 16,161 the fourth highest in the country instead of second. (Pennsylvania ranks eighth with 8,268 deaths, according to Johns Hopkins.)

The rising case numbers in this region have not been reflected in death tolls to date; the number of daily deaths in Pennsylvania has been fairly steady since late July, though the average slightly increased from 11 deaths a day as of Sept. 30 to 19 a day as of Wednesday. The number of deaths has been consistent in New Jersey since August and averages four per day.

Pennsylvania’s average number of new daily cases has jumped 16% in the last week and New Jersey’s has increased by 21%, according to an Inquirer data analysis. Both states had about 3.7% of tests coming back positive this week.

Though some of the spread is linked to students returning to college towns, Wolf and New Jersey Gov. Phil Murphy on Thursday each said they could not fully explain the increase.

Contact tracing has not indicated the spread is being driven by K-12 schools or indoor dining in either state, officials said.

“I think there is a concern generally that we’re going to see an upsurge as we get into the flu season and colder weather,” Wolf said at a news briefing. “I think that might be part of it. I think part of it is Pennsylvania has a lot of colleges and universities and they’re back in session.”

However, Wolf said the state was in a “very different situation” from the pandemic’s onset because it has a substantial store of personal protective equipment and ventilators and because most residents are complying with public health guidance and wearing masks.

New Jersey officials were slightly more grim, warning that hospitalizations are rising and that the state might not be able to get backup from its neighbors if health-care workers fall ill, as it did in the spring. The state has a stockpile of supplies.

The case increases, Murphy said, were not surprising based on scientific modeling, but the numbers are a bit higher than what was projected. Officials said they are seeing increasing signs of community spread in the state.

The day’s unusually high count in New Jersey was partially explained by previously identified outbreaks in certain counties: Nearly a quarter came from Ocean County, where Murphy said it was possible more people were going in for testing after recent Jewish holy days.

Gloucester County, which has likewise seen an increase, reported 114 new cases Thursday, 89 of which were in people age 17 to 22, according to the county. They were mainly associated with Glassboro, which is home to Rowan University; the state is also working with Monmouth and Rutgers Universities to expand testing amid case increases in their host counties, Persichilli said.

Officials are also watching rising case numbers in Bergen, Essex, Passaic, and Union Counties, each of which reported more than 80 new cases Thursday.

“To say this virus isn’t still with us, to say it’s not virulent, to say it could not take your life, is completely false," Murphy said.

Staff writers Bethany Ao and Laura McCrystal contributed to this article.