The island communities in Malaysia heavily depend on diesel or combined solar-diesel power plants. High cost of diesel, difficulties of transporting diesel during the monsoon seasons, low and variable solar flux, and the high maintenance cost of solar cells and batteries are perennial issues associated with these conventional energy systems on the islands. Hence, the next resort is to rely on renewable energy from the sea. However, Malaysian coastlines have low wave heights and low current speeds, giving rise to more challenges in optimizing devices for extracting wave and tidal energy sources. This paper presents study on the development of a combined offshore energy harvesting system in Malaysia seas condition. The main objectives are to develop, construct, and test a prototype demonstrator and test platform of the Combined Ocean Renewable Energy System (CORES) for the Malaysian sea. In order to harvest large power from the ocean, CORES combines wave and current devices on the same shared floating platform. Wave and tidal energy data from the chosen site location, Pulau Tinggi, in the state of Johor, Malaysia was assessed to estimate the output power to be produced. Meanwhile, a comprehensive study was conducted to optimize the CORES concept to verify its reliability, safety, and cost-effectiveness. Numerical simulations on the behaviors of the platform and oscillating water column, point absorber, savonius current turbine and solar devices were carried out at Marine Technology Centre at Universiti Teknologi Malaysia. Finally, a full scale prototype was built and deployed near an island in the South China Sea. The findings in this research are expected to bring significant reference towards more reliable large-scale ocean energy systems for the welfare of island communities in the tropical regions.