The purchase is envisioned as a component of a more expansive trade deal if the world’s two largest economies can reach an agreement in the next few months.

China will need an estimated 8,800-plus planes over the next 20 years to meet rising demand for air travel, according to Boeing’s commercial- market outlook. About 60% of that demand would come from airlines expanding their fleets, while airlines replacing older jets with more fuel-efficient models would account for the rest.