During his bilateral meeting with South Korea President Moon Jae-in on Monday, Duterte said he was hopeful that South Korean investors would pour in more investments in manufacturing, automotive, food production and processing, agribusiness, electronics and energy.
The two leaders will both attend the APEC summit of Asia Pacific leaders in Vietnam's central city of Danang.
Moon said he feels the Seoul-Beijing relationship is making a new start toward a new era.
President Moon Jae-in and Chinese Prime Minister Li Keqiang reaffirmed their efforts Monday to quickly normalize the countries' ties soured by the deployment of a US missile defense system in South Korea, while the Chinese premier noted a "bright" future for their bilateral relations.
For months, China enforced what many believed to be de facto economic retaliation against South Korea that included a ban on large group tours to South Korea and a range of non-tariff import barriers that effectively prevented shipments of many South Korean products, such as cosmetics.
China and South Korea have agreed to restore bilateral relations to a "normal development path swiftly", the foreign ministry in Seoul said in a statement in October.
The leaders "shared the view on the need to stably manage the current security conditions on the Korean peninsula in relation to North Korea's nuclear and missile programmes, and agreed to seek to peacefully resolve the North Korean nuclear issue through dialogue", the office said.
"I am confident about the China-South Korea relations because their [industrial] structures are strongly complementary", Li was quoted as saying, adding a "new horizon" will open for the countries' bilateral relationship.
"There are signs of cooperation and improving relations between China, South Korea and Japan".
But Cui Zhiying, an global relations professor at Tongji University in Shanghai, took a more cautious view.
Also on Saturday, the US and South Korea launched a joint naval drill in a show of strength against the North's leader Kim Jong-un.
And after his fiery speech in Da Nang on Friday, Trump arrived in the Vietnamese capital Hanoi on Saturday, where he described Xi as a "good man" who "wants to do right".