The ships are awaiting permission to dock at a safe southern European port to disembark their passengers.
ADVERTISEMENTHumanitarian ships rescued over 700 migrants off the coasts of Libya and Malta in just one weekend, NGO SOS Mediterranee said.
The migrant aid group said its Ocean Viking vessel had conducted six operations in international waters since Saturday.
In the last operation, it rescued 106 people off the Maltese coast after being alerted by German aid group Sea Watch, the group said.
"The youngest survivor rescued in this operation is just 3 months old," SOS Mediterranee tweeted.
Just a few hours before, the Ocean Viking joined vessels from Sea Watch and ResQship, another German group, to rescue about 400 people "from a large wooden boat taking on water" in the central Mediterranean, the group said.
Ocean Viking alone has 555 passengers on board from this weekend's operations, including at least 28 women, two of whom are pregnant.
The group has yet to determine at which safe European port they will be able to disembark.
According to the International Organisation for Migration, an estimated 1,113 deaths were recorded in the Mediterranean in the first half of this year -- that is more than twice the numbers recorded over the same period last year.
The central Mediterranean crossing, between Libya and Italy or Malta, is by far the deadliest in the world, with 930 deaths recorded there.