The mayor of West Chester declared a state of emergency on Friday as the number of COVID-19 cases there has doubled over the last month, and more than tripled among those ages 18 to 22.

Under the declaration, the borough is restricting social gatherings at private residences, requiring mask wearing, and instituting $300 fines for those who don’t comply.

Mayor Dianne Herrin said the infections among young people are concentrated in rental areas near West Chester University. She couldn’t say how many living there are West Chester students.

Local officials have become increasingly concerned about the rising case numbers and behavior in that area, she said.

“We are seeing a lot of activity, outdoor gatherings that are quite large, with close contact over long periods of time and no mask wearing,” Herrin said.

West Chester, the largest of the 14 Pennsylvania state universities, with more than 17,700 students, is conducting classes remotely this semester, but 552 students are living on campus and many more reside in the surrounding neighborhood.

According to data from the Chester County Health Department, from August to September the number of positive COVID-19 cases in the borough rose from 202 to 437. In the 18-to-22 age category alone, cases more than tripled from 88 in August to 299 in September. That age group makes up 68% of all COVID-19 cases in the borough.

The university has a record of 103 students who said they tested positive for COVID-19 from mid-August to Sept. 27, university spokesperson Nancy Gainer said. Eleven of them reside on campus, she said.

West Chester, however, is not testing students for the virus, like some other universities, including Pennsylvania State University, Swarthmore College, and Ursinus College. The university is relying on students to self-report, Gainer said, adding that the university is ready to comply with the order.

“The university will wholeheartedly support it and strictly enforce it and push the messaging out to students,” she said.

Herrin said she understands the university is in a difficult position without control over off-campus rental units or whether students choose to rent them. That’s why the borough is stepping in, she said.

“It has to be a partnership between the university and the borough, and that’s what we’re really working to achieve,” she said.

Under the state of emergency, Herrin said, all social gatherings at private residences must be limited to no more than 10 people. If there are already more than 10 people living in a house, no other people are permitted to gather at the residence, either inside or outside.

Those who violate the mandate will be cited $300 per person for each individual gathered at a residence above the limits, including the host.

The declaration also mandates that anyone in West Chester wear a face mask when within six feet of other people if they are inside public buildings; on public transportation and rideshares; waiting to enter buildings or public transportation; or in contact with people outside their household, indoors or outdoors. The borough will issue a $300 citation for infractions. The restrictions do not impact restaurants, which are under state guidelines and which were open and active for First Friday.

The declaration lasts for seven days and could be extended, she said. Some residents have complained that the declaration violates their rights, she said.

“This is a temporary and very minor sacrifice for us all to make to protect our friends and neighbors and prevent them from getting sick,” she said.

West Chester was the first university in the region to cancel in-person classes in March as the pandemic was taking hold in the region, and its move proved prescient, with most other schools following. Gainer said that even after the borough’s first emergency declaration expired in March, the university followed up when it got reports of students not wearing masks or failing to socially distance.

And West Chester has sanctioned students who have not followed rules. There have been 13 temporary removals from on-campus housing, she said.

At Penn State, 10 students have been suspended for the rest of the academic year and an additional 17 have lost their housing for failing to follow coronavirus safety rules, the university said this week.

Since students returned Aug. 17, the university, which is conducting some in-person classes, has issued 1,277 sanctions for refusing to wear masks in public, violating quarantine and isolation rules, and attending prohibited gatherings on and off campus.

Coronavirus cases at the state’s flagship university have risen to 2,678 as of Friday, up 203 from Tuesday, according to the university’s dashboard. The university, which continues to hold some in-person classes, reported that 638, or nearly a quarter of the cases, are active.

Also on Friday, Lehigh University announced it was scaling back campus activities, including athletics, and increasing testing after a concerning rise in COVID-19 cases. The school recorded 22 new positive cases on and off campus since Thursday and has 250 students in quarantine because they are close contacts to known or suspected cases.

The university also saw an increase in the percentage of asymptomatic students testing positive in its random testing. About 4% tested positive in the most recent round, up from less than 1%.