Borneo is surrounded by the South China Sea to the north and northwest , the Sulu Sea to the northeast , the Celebes Sea and the Makassar Strait to the east , and the Java Sea and Karimata Strait to the south . by the South China Sea to the north and northwest , the Sulu Sea to the northeast , the Celebes Sea and the Makassar Strait to the east , and the Java Sea and Karimata Strait to the south .