Rajang river trip.....The Rajang River or known as Sungai Rajang is a river in Sarawak, Malaysia. The river is located in northwest of Borneo and it originates in the Iran Mountains. The river flows approximately 563 km to the South China Sea, making it the longest river in Malaysia. The upper part of Rajang River is also known as Batang Balui by the Orang Ulu. Some of the more important tributaries are the Katibas River, the Balleh River, the Bangkit River and the Kanowit River.