Initially postponed due to coronavirus, the deployment of US Marines to the Top End is back on, but questions remain about how many are coming, when they'll arrive or where they'll be treated if any contract COVID-19.

Around 2,500 Marines were expected to arrive in Darwin in early April as part of an annual rotation to the Top End that has taken place since 2012.

But the risk of spreading COVID-19 into the Territory and its vulnerable remote Aboriginal communities was considered too great at the time.

Defence Minister Linda Reynolds today informed US Secretary of Defense Mark Esper the military contingent had now been given approval.

The size and date of the deployment have yet to be determined, although the Marines usually stay in the Top End throughout the dry season. NT Chief Minister Michael Gunner welcomed Ms Reynolds' announcement and said local businesses would get a "massive boost" by having the Marines in the Top End.