Philadelphia surpassed 30,000 confirmed coronavirus infections since March and New Jersey’s average number of new daily cases hit its highest peak in a month Wednesday, while outbreaks traced to house parties led officials to again warn against indoor gatherings.

A “worrisome” pattern of community clusters has emerged in New Jersey, said Gov. Phil Murphy, many of them related to people getting together at parties or other events.

After one recent party in North Jersey, 55 people fell ill with the coronavirus, Health Commissioner Judith Persichilli said Wednesday. Among the new outbreaks was one affecting the Rutgers University football team, which the school said Saturday was quarantining: 15 players have now tested positive, Persichilli said.

When many people crowd into an indoor, air-conditioned space, Murphy said, “you have also invited coronavirus to your party.”

And Pennsylvania’s seven-day average for new daily cases was climbing closer to 1,000, continuing an increasing trend that has not dropped or even plateaued since late June. The state reported 834 new cases Wednesday. Philadelphia reported 132, and Delaware County, which has experienced the sharpest recent increase in cases of the suburban counties, reported 63.

The United States also reached another grim milestone: The death toll surpassed 150,000, according to Johns Hopkins University data. That represents just under a quarter of all deaths worldwide.

The countries with the next-highest death tolls are Brazil, with more than 88,000, and the United Kingdom, with more than 46,000. China, where the virus was first identified, has reported 4,658 deaths.

Florida, North Carolina, and California set new single-day records for the number of deaths reported, and infectious-disease expert Anthony Fauci warned leaders in states where cases have begun to increase to get ahead of the curve if they want to avoid ending up in the same place.

In New Jersey, Murphy had a similar warning. On July 22, the state’s seven-day average for new daily cases was 192. That has climbed over the last week to 426 — the highest it has been in a month, since it hit 556 on July 1, according to data analyzed by The Inquirer.

It was the last four days, which added about 2,000 new cases, that set the state back nearly to where it was a month ago, Murphy said Wednesday. The transmission rate remains just over one, meaning at least one person is being infected as a result of each new case, but has not climbed higher.

“Over the past four months we have crushed the curve,” Murphy said. “But folks, this is sobering. … We can’t go backwards. We can’t afford to go backwards.”

And, the governor suggested that as the state continues to lose ground in keeping new case numbers low, that could further delay the return of indoor dining.

“I’m not going to say that indoor dining is like a house party, because it isn’t,” Murphy said. “But when one party in an air-conditioned house leads to dozens of new cases, it should give us all pause.”

Hospitalizations in New Jersey continued to drop, Persichilli said. But South Jersey is reporting a positivity rate that is higher than the state’s average, meaning a higher percentage of people are testing positive there than in north or central Jersey.

Murphy acknowledged the hot weather was likely driving people into enclosed, air-conditioned spaces and said he understands that people need to “blow off some steam with friends.” But gatherings are “how coronavirus gets passed around more efficiently,” he said.

Health experts across the country have asked people to socialize outdoors or stay inside with members of their household to prevent the spread of the virus, particularly as they have learned more about its airborne spread, and contact tracers, including in New Jersey and Pennsylvania, have tracked infections to indoor gatherings based on patient reports. On Wednesday, Fauci told Americans to avoid bars and large gatherings as he advised them on how to help stop coronavirus surges in their states.

After New Jersey last week allowed parents to opt for virtual-only learning for their children, some Democratic state lawmakers said Wednesday they would introduce legislation to require public schools to start the school year with only remote instruction.

The state has directed schools to open with a hybrid in-person and virtual model, though parents can choose virtual-only.

The bill will propose that state officials evaluate to determine whether buildings can reopen based on virus infection statistics starting Oct. 31, meaning schools would be able to stop virtual-only learning if it became safer to do so.

Murphy declined to comment on the proposal during his Wednesday briefing, saying there was a “strong chorus on both sides.” The lawmakers behind the bill said students and teachers shouldn’t return to school until their safety can be ensured.

The Philadelphia School District, which announced Tuesday that it would start the school year with only virtual classes, plans to provide internet access to all families, the superintendent said Wednesday.

The district will soon announce details of the plan, which will connect every student who needs it to the internet, Superintendent William R. Hite Jr. said.

In Philadelphia, none of the Phillies players and coaches — who played the coronavirus-stricken Miami Marlins on Sunday — had tested positive on either Monday or Tuesday. But Eagles offensive tackle Lane Johnson announced he had contracted the virus.

The Pennsylvania Interscholastic Athletic Association board of directors voted unanimously Wednesday to proceed with fall high school sports.

The PIAA announced earlier this month that it was planning for the “normal start of the fall sports season unless otherwise directed by the Commonwealth.”

Wednesday’s vote, which was reported by EasternPAFootball.com, means football teams can begin official workouts on Aug. 10, and the other fall sports can start Aug. 17.

Contributing to this article were staff writers Rob Tornoe, Melanie Burney, Laura McCrystal, Kristen A. Graham, Robert Moran, EJ Smith, and Scott Lauber.