A nuclear test by North Korea would be a "game changer" in the region and provoke a US response spanning "multiple instruments of national power," officials with the US Indo-Pacific Command in Honolulu said Friday.

North Korea, which has carried out four ballistic missile launches this week, appears to be preparing for a nuclear test that would likely take place one to two weeks after the Chinese Communist Party congress starting on October 16, an official who requested anonymity told reporters.

The official's analysis echoes that of the South Korean intelligence services, who believe a test is likely between October 16 and the US midterm elections on November 7.

While acknowledging that a link had not been established between the recent launches and a possible nuclear test, the head of the American fleet in the region, Admiral Sam Paparo, said any such test would be a "matter of grave, grave concern," and would prompt a broad US response.

"That response would be first in close consultation with our treaty ally, South Korea, and would likely be in accordance with our doctrine of integrated deterrence -- it would span multiple instruments of national power," he said, alluding to diplomatic, military and economic measures.

General Kenneth Wilsbach, commander of the US Air Force in the Pacific, said North Korea's possession of such a weapon was especially unsettling because, unlike other powers, Pyongyang did not consider nuclear arms to be strictly deterrents -- kept but never used.

"They've threatened to use those weapons against their neighbors, and possibly even the US," he said. "I mean, if you think about other countries who have those weapons, they don't talk like that. And so that should have everyone concerned."

Wilsbach said he "would not be surprised if we saw some sort of test in the near future," adding that, were one to go ahead, it would "certainly be a game changer" in the region.

"And it would be of great concern to a number of countries," he added. "I suspect that even China and Russia would be concerned about that."

Under pressure from international sanctions over its weapons program, North Korea adopted in September a resolution proclaiming itself an "irreversible" nuclear power.

Pyongyang has carried out six nuclear tests since 2006, with the most recent -- and most powerful -- in 2017.

Satellite images taken in recent months show signs of activity in a tunnel at the nuclear test site Punggye-ri.