AJO, Ariz. — Motels, mobile home camps and Airbnbs in this small Arizona border town are full up. Work crews stream into eateries for takeout orders. License plates on trucks parked outside the crowded laundromat come from as far away as Alaska.

Around the country, some states have cut back on construction activity to curb the spread of the coronavirus, and hotels and restaurants in many cities have closed. But here in Arizona, the federal government is embarking on a frenetic new phase of construction of the border wall.

The Trump administration contends that the wall will help prevent the spread of the virus into the United States from Mexico, though epidemiologists and the director of the Centers for Disease Control and Prevention say such a barrier would not mitigate the outbreaks already occurring in every state.

The intensification of construction during the pandemic is raising fears among residents of Ajo, Ariz., and other nearby border communities that the growing influx of workers increases their risk of exposure. Some disease specialists in Arizona are warning that workers clustered in tight quarters along the border could spread the virus around the country when they return to their families.