Thirty minutes into the violin lesson, Anthea Kreston knew that something was wrong.

Ms. Kreston, an acclaimed American violinist, was at home in Corvallis, Oregon. Her student, Yunhe Tang, a talented 14-year-old who prefers the name Kevin, was at his home in Chengdu, in southwest China. She had been giving Kevin violin lessons via Skype once a week since last August, but today something was different. Kevin seemed lethargic, like he hadn’t practiced, and Kevin always practiced.

“He said, ‘Well, I’m not having lessons here, and I’m not going to school,” Ms. Kreston said. “And then he went, ‘Everyone’s sick.’”

It did not take long for Ms. Kreston to realize Kevin’s life had been affected by the coronavirus, even though he lived over 700 miles from Wuhan, the city at the center of the outbreak.

Chengdu is one of dozens of Chinese cities that are effectively on lockdown because of the virus. Schools are closed for the rest of the month and most businesses are struggling to reopen after being closed for weeks. Sichuan, the province of which Chengdu is the capital, had 436 confirmed cases of the virus as of Wednesday.