Indonesian rescuers on Thursday intensified and expanded search and rescue mission for 17 crew members, who have gone missing after a cargo boat went down in water off Central Sulawesi province of central Indonesia, a senior rescuer said.

KM Lintas Timur cargo boat sank on Saturday but was known until Tuesday after one of all 18 crew members on board was rescued by an Indian ship NV Nurbayaksar, the crew member named Yakob informed about the incident, Basrano, head of search and rescue office in the provincial capital of Palu said.

The search and rescue operation was carried out through air and waters, involving a plane, a helicopter, and several ships, he said.

"We also include personnel from air force and navy and those from the company operating the cargo boat PT Citra Baru Adi Nusantara in this operation," he told Xinhua via phone from the scene.

The water territory between Bangai Kepulauan and Luwu is determined as the focus of the operation, said Basrano.

"This has been the sixth day of the incident, based on a calculation and the movement of current, an object commonly moves toward the territory," he unveiled.

Still, recurrent rains and huge waves pouring and striking the area are hampered the visibility and movement of the rescuers, Basrano said.

Under the country's law, the rescuer said the mission will be carried out for seven days since the incident, nevertheless the period can be extended or shortened in accordance with the situation.

Boat is a favorite transport mean in the vast-archipelagic nation, home to over 17,500 islands. However, lack of implementation of safety standard has often triggered incidents at sea.