He said, "Multilateralism and the free trade system is under attack, factors of instability and uncertainty are numerous, and risks and obstacles are increasing".
But none addresses USA complaints about its technology policy that prompted Trump to impose penalty tariffs of up to 25 percent on $250 billion of Chinese imports.
About 3,600 companies from more than 170 nations, regions and worldwide groups are taking part in the country's first national-level expo for imports, the Chinese government said. "Inclusion and reciprocity, win-win and mutual benefits are a widening road".
China's imported goods and services are estimated to exceed Dollars 30 trillion and Dollars 10 trillion respectively in the next 15 years, Xi said in his inaugural address, state-run Xinhua news agency reported.
China's shift to an import model is "going to be a huge pain for a lot of businesses, but it's also going to make a good opportunity for a lot of consumers", he said. The government has already cut tariffs this year and said it would do so again.
Xi said measures announced in April to relax access to Chinese market have so far been implemented. He did say, however, that stimulus already announced was being seen in the economy.
Instead, people involved in planning meetings have said they were anticipating an event long on symbolism and short on substance meant to signal China's willingness to narrow trade deficits and openness.
Enthusiasm wasn't high in the run-up to the event.
Kenya was ranked position 61 overall out of a total of 190 economies and the seventh most improved country globally. Starbucks Corp CEO Kevin Johnson, whose company opens a store in China every 15 hours, won't be attending even though he'll be in the same city.More news: Raheem Sterling to become 'ultimate footballer' at Man City, says Darren Bent
Ma, who recently took back an earlier pledge to create a million jobs in the USA - blaming the trade war launched by Donald Trump - made the comments in a panel discussion at the massive expo in Shanghai. While the American President has floated the possibility of a deal when he meets his Chinese counterpart, Xi Jinping, in coming weeks, the two countries remain far apart on everything from market access to government support for state-run enterprises.
While Xi didn't mention Trump or the United States by name, the trade conflict was a clear theme in his remarks.
Decrying "protectionism", "isolationism" and confrontation, Mr Xi said countries should fix their own houses before targeting others.
"They should not hold a flashlight in hand, doing nothing but highlighting the weaknesses of others and not their own", he added.
In a speech at Davos almost two years ago, he presented China as a beacon of globalisation, in a counterpoint to Trump. "We've taken the toughest-ever action to crack down on China's abusive trade practices".
International Monetary Fund chief Christine Lagarde also said there remained "room for even greater reform" in China's market.
About 180 United States companies are sending representatives, including big names such as Alphabet Inc's Google, Boeing Co, Caterpillar Inc, Facebook Inc, General Motors Co, Honeywell International Inc, Microsoft Corp, Tesla Inc and Qualcomm Inc.
In addition, China would open up its lucrative domestic health care and education sectors, financial services, telecoms and mining, to foreign investors, Xi said.
They noted China is an important and promising market, and they will tap the potential for cooperation and promote bilateral trade growth and the development of free trade globally.