■ David Collins: A fragile Block Island braces for the worst.

O ne measure of the level of coronavirus anxiety on Block Island was a recent incident in which someone threatened to sabotage the power company transformers, to create a blackout that would keep outsiders from coming to the island.

I know it sounds a bit farfetched, but island police Chief Vincent Carlone called it a “serious domestic terror threat” in a statement to The Block Island Times.

The incident was reported to the FBI and security teams were posted at the power company, the chief said.

Block Island, like its bigger sister New England resort islands to the east, Nantucket and Martha’s Vineyard, finds itself in an especially vulnerable position as the coronavirus pandemic starts lapping at its shores.

On the one hand, the offshore islands seem like a great and safe place to ride out the storm, isolated, underpopulated and, at this time of year, the epitome of social distancing.

Indeed, that has been drawing owners of second homes there back from the cities. The private jets have been filling the tarmac at Nantucket’s airport.

And yet the remote nature of the islands is precisely what makes them especially fragile in a growing coronavirus pandemic.

The new hospital on Nantucket has no intensive care facilities and only three ventilators. Block Island has only a medical center with a few examining rooms.

The medical infrastructure of these islands depends on evacuation to the mainland for serious emergencies.

Fishers Island, which also is seeing a return of summer people, many from the hot spot of New York City, shares the same predicament, although evacuations might be easier, given the island’s closer proximity to the mainland.

If there were a growing medical emergency on the mainland, any island evacuations could become more tenuous. A hospital doctor on Nantucket told The Washington Post there have been discussions about how they might ration medical care in life-or-death treatment choices on the island.

This worry helps explains why the Block Island Town Council this week unanimously adopted a draconian emergency ordinance, summoning what authority it has to shut down the island as best it can.

While the council couldn’t prevent travel to the island, the ordinance discourages visits by nonresidents and orders nonessential visitors to leave.

Everyone is ordered to shelter in place and anyone arriving must self-quarantine for two weeks.

The order also addressed one issue of particular concern to residents: the off-island workers who commute to island construction sites by plane or ferry. Construction sites essentially are shut down, and only transient workers for essential services may commute to the island.

Hotels, bars and restaurants are all closed except for takeout.

The Block Island council order lasts until April 15. After that, the island’s economy, which depends on visitors, certainly will begin to choke.

I wrote last week about the summer people who have started to return to their weekend and vacation homes here on the Connecticut shoreline. I have since heard from some readers concerned about the potential exposure they bring from hot spots.

I would hope these returning homeowners would follow self-quarantine guidelines, and I suspect most will. They’re here because they are serious about being safe.

A gentleman in front of me in the prescription pickup line at CVS on Wednesday, wearing winter gloves and keeping his distance, mentioned something about his Manhattan pharmacy.

I took another step back. But his obvious caution, on a necessary errand, was reassuring.

We’ll all be fine if we keep respecting one another.