Philippine President Rodrigo Duterte on Thursday ordered the occupation of uninhabited islands and shoals it claims in the disputed South China Sea, asserting Philippine sovereignty in an apparent change of tack.

The firebrand leader, who on the campaign trail joked that he would jet ski to a Chinese man-made island in the South China Sea to reinforce Manila's claim, also said he may visit a Philippine-controlled island to raise the national flag.

"The unoccupied, which are ours, let's live on it," Duterte told reporters during a visit to a military base in Palawan, near the disputed waters.