By Agence France-Presse
Duterte has in his 10 months in office sought to weaken ties with the United States, the Philippines' mutual defence treaty partner and former colonial ruler that he has said is diminishing as a global superpower.
The 12-day "Balikatan" war games that opened on Monday will involve fewer than half the number of soldiers than in 2015, when they were steered by Duterte's pro-American predecessor, Benigno Aquino.
There will also be no focus on boosting the Philippines' maritime defence capabilities, which in previous years had been widely seen as a show of strength against Beijing over competing claims in the South China Sea.
Duterte has reversed Aquino's policy of challenging China forcefully on the territorial row, electing to instead pursue closer economic, political and military relations with Beijing.
While on a trip to Beijing last year Duterte, a self-described socialist, announced that he was in the "ideological flow" of China's communist rulers.
Much of Duterte's criticism appeared to have been triggered by American criticism of his drug war, which has claimed thousands of lives and been condemned by rights groups as a possible crime against humanity.
Focus on China, Russia
Duterte responded to criticism from then-US president Barack Obama by describing him using an offensive epithet and threatening to sever defence relations completely between the two nations.
Bilateral ties have warmed under Obama's successor, Donald Trump, but Duterte has continued to signal his preference for building stronger relations with China and Russia.
Duterte is due to next week visit China for a second time as leader, and is also expected to this month travel to Moscow for a meeting with Russian President Vladimir Putin.
Duterte last week said he may be too busy to accept an invitation by Trump to visit Washington, even though no date had been proposed for the trip.
Previous editions of the Balikatan exercises involved large-scale joint operations in or near the South China Sea, which China claims nearly in its entirety.
This year the exercises will focus only on counter-terrorism and disaster relief, the heads of the Philippine and US delegations said at the opening ceremony at the national military headquarters in Manila.
They will involve 2,600 American soldiers and 2,800 Filipino troops, according to both sides.
This is down from 12,000 in the 2015 edition of Balikatan, which means shoulder-to-shoulder.
The American co-director of this year's Balikatan, Lieutenant General Lawrence Nicholson, said the US military hoped the exercises would grow again in future editions.
"If you look back on 33 years of Balikatan, they are all different. There are any number of ways it can change. It can be bigger, it can be smaller. We hope it gets bigger," Nicholson told reporters.
One of the major exercises this year will simulate a response to a major storm hitting the eastern Philippines, then cutting across heavily populated areas of the country including Manila.
The Philippines endures about 20 major storms a year that sweep in off the Pacific Ocean, many of them deadly.
American military aid played a crucial role in saving thousands of lives after Super Typhoon Haiyan, then the strongest storm ever recorded to make landfall globally, hit the Philippines in 2013.
More than 7,300 people died then but the death toll would have been far higher if US warships did not quickly reach the devastated areas and deliver supplies.