A new contingent of US Marines are headed to Darwin in the eighth rotation of American troops training down under.

The ramp-up from 1700 Marines expected to arrive this year to 2500 will be the first time US troop numbers reach the full planned complement.

The Morrison government says the increased US military presence was the result of Australia's strong alliance and friendship with the US.

This year, the Marines will participate in multiple training activities with Australian troops, including a new humanitarian assistance and disaster response segment.