Migrants and refugees get on a ferry to Turkey at the port of Mytilene in Lesvos, Greece on Oct. 5, 2016. (Xinhua/Anthi Pazianou)

ATHENS, April 24 (Xinhua) -- The death toll in the refugee boat tragedy unfolding off Lesvos island in the Aegean Sea has risen to eight, the Greek Shipping Ministry announced.

Among the victims there are an underage boy and four women, while a pregnant woman was rescued and transferred to a local hospital on a Swedish Frontex vessel, Greek Coast Guard said.

A rescue operation is underway to locate missing persons, while it was still unclear how many people were on board when the boat capsized.

According to the pregnant survivor's testimony, there were 25 people on board when the vessel left Turkey's shores, Greek national news agency AMNA reported.