The United States has dispatched its top diplomat overseeing arms sales to promote American weaponry at the largest air show in Asia, where China's military footprint and political influence are surging.

Ambassador Tina Kaidanow told reporters that a large U.S. delegation at the Singapore Air Show is doing "everything we can" to encourage Southeast Asian governments to purchase U.S.-made arms like the F-35 fighter jet.

Washington has been seeking to woo countries like Vietnam, a former foe, with arms sales and transfers at a time when China has bolstered its territorial claims in the South China Sea with construction on man-made islands.

Kaidanow said the transfer last year of a coast guard cutter to Vietnam, which often contests China's maritime claims, was an "incredible positive."

"They will be able to use our equipment for maritime domain awareness, for maritime security ... that's important for them," said Kaidanow, who visited Hanoi last week shortly after U.S. Defense Secretary Jim Mattis, on a visit to Vietnam, announced plans to send an aircraft carrier to the country in a show of solidarity.

"Our hope is they will consider American companies (not only) in defense but in other sectors as well," Kaidanow said, referring to Vietnam.

China's assertive military posture in the South China Sea has concerned several Southeast Asian countries with rival territorial claims, but Beijing has at the same time offered infrastructure investment across the region as a way of winning friends.