The US Navy's top officer says it was unsafe and unprofessional for a Chinese naval warship to sail across the path of a US vessel in the Taiwan Strait last month.

Chief of Naval Operations Michael Gilday made the comment in an interview with NHK in Washington on Tuesday.

Admiral Gilday said the maneuver was dangerous and it was not what is expected from high-end navies in terms of acting responsibly at sea.

Admiral Gilday said there are no indications right now that China will attempt to unify Taiwan by force.

But he said he takes very seriously the US intelligence assessment that Chinese President Xi Jinping has instructed the military to be ready by 2027 to invade Taiwan.

Admiral Gilday said the US forces have to be ready for that possibility every single day, whether a contingency is to occur in 2027, or 2030.

But he added their focus is on deterring that conflict from ever happening.

Admiral Gilday stressed the importance of cooperation between allies and partners not just in conflict, but also on a day-to-day basis to ensure that the Indo-Pacific remains open and free. He said the US-Japan relationship is the cornerstone of stability in the Western Pacific.