Pence warned Saturday that United States sanctions and pressure on China would remain in place until Beijing reforms its trade practices.
He denied there was a "hidden geopolitical agenda... nor is it a trap as some people have labelled it".
A USA official told reporters that Pence was "currently having a "pull-aside" with the Taiwanese head of delegation to APEC Morris Chang".
Mr Pence also had stinging remarks for Xi's Belt-and-Road Initiative, which Morgan Stanley says may total US$1.3 trillion by 2027 - dwarfing the funds the and allies have mobilized.
Trump is set to meet Xi at the G20 summit in Argentina next month.
Republican firebrand Donald Trump has escalated trade tension with Beijing this year, hitting Beijing with tariffs on $250billion (£195billion) of Chinese imports.
"We've put tariffs on US$250 billion (RM1.04 billion) in Chinese goods and that number could more than double", he said.
Not so, Trump and Pence protested.
He said the wasn't in a rush to end the trade war and would "not change course until China changes its ways" - a worrying prospect for a region heavily reliant on exports.
"We have taken decisive action to address our imbalance with China", he said.
Controversially, Mr Pence said the U.S. saw ASEAN as an "irreplaceable strategic partner".
Can the United States and China resolve their differences? "So, I don't think there's a timetable".
U.S. officials have warned China poses the most significant global threat to the US. "Attempts to form exclusive blocs or impose one's will on others should be rejected".
Pence said on Saturday the U.S. would partner with Papua New Guinea and Australia in redeveloping the Lombrum Naval Base on Manus Island.
In addition, the Chinese leader called for "an open, inclusive and transparent approach" to various free-trade arrangements.
"Tit-for-tat protectionism and threats of trade wars are in no one's interest economically and undermine the authority of the global and regional trade rules that benefit us all", said Scott Morrison.
"Great power competition between the United States and China in this region doesn't have to mean hostility", Mr Pence said.
Pence is representing Trump at the summits after the president opted not to attend - becoming the first USA head of state to skip the marquee Asian conferences since 2013.
But he has also broken somewhat from the president on a few occasions, including during the 2016 campaign in the wake of the infamous Access Hollywood tape in which Trump described how his celebrity status allowed him to "grab [women] by the pussy".
"I conveyed to President Xi our significant concerns over land reclamation, construction and the militarization of disputed areas, which makes it harder for countries in the region to resolve disagreements peacefully", Obama said back then.