Seven people were killed and 15 others went missing when a ship carrying 132 people capsized off the Indonesian part of Borneo island, police said on Saturday.
The ship sank Friday moments after it left a harbour in Tapin district where it picked up additional passengers, said Rastam Hadi, a police officer.
The captain of the ship, who was among the 110 people surviving the accident, was detained for questioning, police chief Rizqi Maulana told the state-run Antara news agency.
Maulana said the ship was designed to carry 45 passengers.
"Because there were too many passengers, the ship lost its balance and water entered the cabin," the police chief was quoted as saying.
Indonesia, the world's largest archipelagic nation, has seen several major ferry disasters in recent years partly attributed to the lax enforcement of safety regulations.
On Wednesday nine people were killed when a small ferry sank in poor weather off Indonesia's resort island of Bali.