Philippine President Rodrigo Duterte said Tuesday he would soon visit China and hoped also to travel to Russia, as he again criticised longtime ally the United States for "arrogance".

The mission to China will be Duterte's first outside of Southeast Asia since assuming the presidency on June 30, in a symbolic move highlighting the importance he places on improving ties with Beijing that soured over competing claims to the South China Sea.

"China has repeatedly invited me. I have accepted the offer," Duterte said in a speech at the presidential palace.

He gave no specific dates for the visit, but said it would take place before he went to Japan from October 25 to 27.

Duterte said he had originally planned to visit Japan, the Philippines' biggest source of foreign aid, ahead of China.

However he explained that Japan offered a "definite" date, then China told Duterte there was a "vacancy" earlier and so he accepted.

Duterte also said that, after Japan, "probably I will go to Russia".

Duterte has looked to build closer ties with China and Russia, while launching repeated tirades against the United States, the Philippines' former colonial ruler and defence ally.

His tirades have been largely in response to US criticism of Duterte's war on crime, which has claimed more than 3,300 lives and raised fears about extrajudicial killings.

Duterte has cancelled joint patrols with the United States in the South China Sea, said he may scrap a defence pact that allows thousands of US troops to rotate through the Philippines, and threatened to eventually cut ties completely.

Duterte has also branded US President Barack Obama a "son of a whore" for expressing concern about human rights in the drug war.

In contrast, he has described Chinese leader Xi Jinping as "a great president", and praised China and Russia for showing respect in not criticising his crime crackdown.

- 'Arrogant' allies -

Duterte on Tuesday gave another lengthy critique of the United States, branding the nation as "arrogant" and powerless to stop Russia's seizure of Crimea from Ukraine.

He also said the Philippines gained nothing from holding military exercises with the United States, which have been a mainstay of the defence relationship.

"What's the point? They are the only ones benefiting. We are not," he said, as the allies wrapped up a week of war games involving about 2,000 troops in the Philippines.

Duterte had said they were to be the last of his six-year term, putting on ice the 28 exercises they hold annually.

The Philippines had long been regarded as one of Washington's most loyal allies in Asia, with the two nations bound by a mutual defence pact signed in 1951.

Duterte's predecessor Benigno Aquino sought to draw the United States even closer in a bid to counter Chinese efforts to take control of the South China Sea.

China claims nearly all of the sea, even waters close to the Philippines and other Southeast Asian nations, and has in recent years built artificial islands capable of hosting military bases in disputed areas.

The 2014 defence agreement and the joint patrols were key to Aquino's strategy to contain China.

Aquino further angered China by filing a case with a UN-backed tribunal in 2013 against Beijing's claims to most of the sea.

In July, shortly after Duterte took office, the tribunal ruled in favour of the Philippines, saying China's claims had no legal basis and its construction of artificial islands in disputed waters was illegal.

But Duterte vowed not to "taunt or flaunt" the verdict and to seek a "soft landing" with China on the issue.

He has launched negotiations with China over the dispute, a tactic rejected by Aquino.

China has welcomed Duterte's overtures.

"The clouds are fading away. The sun is rising over the horizon and will shine beautifully on the new chapter of bilateral relations," Chinese ambassador to Manila Zhao Jianhua said this month.