About 70 asylum seekers, many of them believed to be children, have been taken to Christmas Island.

The ABC understands the group, comprised of various nationalities, was taken to the island just before 9:00am (local time) on Saturday on board the Navy's HMAS Stuart.

One witness says more than a dozen of the arrivals were children.

The Government is refusing to officially confirm the transfer, saying all details of asylum seeker arrivals are only discussed at the weekly briefings for Operation Sovereign Borders.