"Six were rescued alive on Friday and we continue searching for the 10 people still missing today," Indonesia's search and rescue agency spokesman Muhammad Yusuf Latif told AFP on Saturday.
The group had attempted to swim to nearby Rakata island, he added.
"Six returned to the capsized boat and they were rescued. But the other 10 continued swimming and their whereabouts remain unknown," Latif said.
Rescue teams expanded their search for survivors on Saturday.
Boat accidents are common in Indonesia, a Southeast Asian archipelago of around 17,000 islands, due to lax safety standards.