A new wave of coronavirus has slammed into Philadelphia, with COVID-19 diagnoses soaring to levels not seen since May -- and the city's top health official is asking everyone to cancel family gatherings for the holidays.

Tuesday, the city reported 340 new diagnosed cases of the disease. Over the past week, the city is averaging 296 cases per day.

That's the highest rate since the early peak of the pandemic in the first week of May.

There are increases in coronavirus cases in every age group and every city zip code, said Dr. Thomas Farley, the city's health commissioner.

"I know this is difficult, but we are recommending that people cancel their planned family holiday gatherings," Farley said. "We are not going to get past this epidemic by Thanksgiving, Hanukkah, Christmas.

"Family gatherings right now are simply very dangerous," he said.

Farley said the coronavirus was following the seasonal pattern of similar diseases, including the flu. That means an even higher surge is ahead of us, but likely before widespread use of a vaccine.

"We anticipate further rapid increases of this infection in Philadelphia, which means we are entering a difficult, dangerous period of this epidemic -- possibly the worst period of the entire epidemic," Farley said.

"We need to step up our safety precautions now," he said.

Besides canceling holiday gatherings, he said people should work from home if possible and not get together in person, either casually or for a celebration. Those small group gatherings appear to be spreading coronavirus.

"Don't have a get-together after soccer practice," he said. "Don't join your friends to watch football games on TV."

That difficult, but potentially life-saving, message is true even of big life events that usually bring people together.

"These social gatherings, particularly celebration gatherings, are very dangerous because people get very close and they tend not to wear masks because they want to look good for the pictures," Farley said.

Meanwhile, the state of Pennsylvania is also reporting record levels of new COVID-19 diagnoses. the Department of Health it reported 2,751 additional positive cases of COVID-19, the largest one-day increase yet in the pandemic.

Across the state, health officials are seeing "significant" increases among 19 to 24-year-olds, the Department of Health said in a statement.

Farley said some spread might be occurring in restaurants, though interviews with those who have been diagnosed indicated that the number of possible exposures had increased only sightly.

Deaths and hospitalizations have not risen to peak-pandemic levels, Farley said. The city's hospitals still have room to treat patients, which wasn't the case earlier in the year.

He said the city is finding more people with mild or no infections, which means they may not need to be hospitalized. Plus, hospitals are becoming more familiar with how to treat coronavirus successfully.

He also said there is some indication -- though it has not been proven -- that when people wear masks and stay socially distant they may get a lesser dose of the virus.

"That's yet another reason for everybody to be wearing masks right now," Farley said.