Chinese Foreign Minister Wang Yi says that the Philippines' case against China at an arbitration tribunal over their rival claims in the South China Sea has strained their relations and that it is up to the Philippines to improve ties.

The arbitration case against China in The Hague "is a knot that has impeded the improvement and development of Sino-Philippine relations," a statement on the Foreign Ministry's website cited Wang as saying in Manila.

"We do not want this knot to become tighter and tighter, so that it even becomes a dead knot," Wang, who was in the Philippines for talks on Tuesday, told reporters in Manila. "As for how to loosen or open the knot, (we'll) have to look at the Philippines."