In the days preceding the announcement of the quarantine, the governor had requested that people postpone their visits, “but these aren’t people who will respond to a request,” Ms. Ohashi said while sharing screen shots of heated online debates between incoming travelers and islanders and photos, including one of a tourist raising her middle finger to the protesters, and Facebook comments like “Airline tickets are cheap. It’s exactly why we booked just a week ago. See you soon …”

In a letter to tourism industry leaders on Wednesday, Chris Tatum, the president and chief executive of the Hawaii Tourism Authority, referred to the island’s limited medical capacity. As of March 21, the state had 48 Covid-19 cases.

“We are concerned about the limits of our health care system to adequately care for our community. Visitors putting their plans on hold for the next 30 days will allow our health care providers to manage this pandemic,” he wrote.

That’s the worry of many tourism-dependent communities that don’t have the hospital beds necessary in the event of an outbreak.

On March 16, the 17-bed Moab Regional Hospital in Moab, Utah, a popular adventure destination in southern Utah and the gateway to Canyonlands and Arches national parks, wrote to the Utah governor, Gary Herbert, asking him to shut down tourism businesses to deter visitors. The letter signed by five hospital executives, called the town “ small … cruise ship small … with similar isolation and limitations in resources.”

The next day, the Southeast Utah Health Department instituted a 30-day ban on overnight lodging for nonessential visitors. The parks remain open, and though visitor’s centers are closed, outside exhibits help visitors with logistics.

Of those traveling, many are trying to shelter at second homes where social distancing might be easier than in a city.