Another 23 refugees have left Nauru bound for the United States.

The group includes two Rohingyan families, including a couple with their three children and a father and his two sons.

The rest are Rohingyan, Afghan, Pakistani and Tamil single men, according to refugee advocates.

While well over 300 people have now been transferred to the US under the deal with Australia, more than 1520 people remain in offshore detention on PNG's Manus Island and Nauru.

Thousands of people marched in rallies across Australia over the weekend to mark the fifth anniversary of offshore processing, which began under the Rudd government.