The special zone also would give China a valuable perch to expand its military and intelligence capabilities in Washington’s vicinity, according to American officials who have watched warily as Beijing has invested in at least 60 Latin American port projects.
For El Salvador, the deal came with significant trade-offs, and left several unanswered questions.
The Chinese requested a 100-year lease of a 1,076-square-mile area — 13 percent of the country’s landmass — and demanded tax exemptions for their companies that would last three decades. Details about the financing structure were not publicly disclosed, causing concern among some Salvadorans that their country risked becoming financially beholden to Beijing for generations.
But by the time the United States began its campaign against the Chinese in El Salvador last summer, the Americans had a lot of catching up to do.
To some Trump administration critics, it was a self-inflicted wound.
While the Chinese were offering to build manufacturing plants, invest in renewable energy and make El Salvador a tourist destination, President Trump was calling migrants “animals,” and separating children from parents at the border.
“That attitude opens up space for China,” said Roberto Rubio, director of the National Foundation for Development, a research group in San Salvador, the capital. “If the United States threatens to cut our aid, treats our people poorly and brings little investment, why not go with the Chinese?”
While the Trump administration has suspended aid programs to El Salvador, Honduras and Guatemala, Ms. Ou, the ambassador, noted that China had signed 13 cooperation agreements on infrastructure, investment, science, technology, education, culture and tourism.