MANAGUA, Nicaragua — Doña Albalina Espinoza’s cellphone rattled with the incoming warning call at 2:30 p.m: “The Chinese are coming!” the voice hissed.

Espinoza quickly hung up, then dialed the next number on the list: “The Chinese are coming!” she repeated.

Within minutes, all 150 families in the lakeside village of Obrajuelo had been alerted to the interlopers’ presence.