Sought for comment about the significance of this trip, Cid L. Terosa, senior economist at the University of Asia & the Pacific, said "there seems to be motivating influences" behind Mr. Duterte's visit to Vietnam.
It was unclear whether Duterte's outbursts will affect relations between the two countries, whose militaries have scheduled joint exercises in October. Jointly, Philippines [and] the US?
Despite the territorial dispute with China, the Philippine leader said that he talked to President Xi Jinping and that he "will open all avenues of trade and commerce".
Philippine Secretary of Foreign Affairs Perfecto Yasay Jr., however, contradicted Duterte, saying joint military drills approved by the previous administration will continue until 2017, when they can evaluate whether there's a need for them to go on.
Recounting his meeting with Washington officials, Yasay said he assured them that Manila works within the bounds of the ruling of the worldwide arbitral tribunal on the maritime row to move forward.
"Our focus is on the relationship today and moving it forward", Kirby said at a regular news briefing in Washington.
This week, Duterte said he will open new alliances with China and Russian Federation to increase trade and commerce as defence and foreign ministry officials have started exploring weapons deal with Moscow.
His near-daily outbursts against Washington began in earnest last month, when he spoke of alleged atrocities a century ago by the U.S. when it was the Philippines' colonial ruler.
He told the Filipino community in Hanoi late Wednesday night that he will maintain the military alliance with the USA because of the countries' 1951 defense treaty.
He declared last week he would visit China, with which ties remain frosty over a South China Sea arbitration ruling won by the Philippines in July.
Yasay said he did not bring up the topic of the sea row at the meeting, but USA officials wanted to put it on the table.
PRESIDENT Rodrigo Duterte left the country on Wednesday afternoon to start his two-day official visit to Hanoi, in a bid to strengthen the Philippines' strategic partnership with Vietnam.
He has said he wants USA military forces out of the southern Philippines and blamed America for inflaming local Muslim insurgencies there.
In addition, the Philippine Navy would not take part in South China Sea patrols Duterte said in an hour-long speech reporters described as, "profanity-laced". He said the agreement does not guarantee that the USA would come to Manila's defense if the Philippines was attacked.
Beijing claims around 90 percent of the South China Sea despite other Asian counties considering some of its waters, islands and reefs as their territory.
The two countries also have an Enhanced Defense Cooperation Agreement (EDCA), an executive agreement that gives USA troops, planes and ships increased rotational presence in Philippine military bases, and allows Washington to build facilities to store fuel and equipment there.