The president was quick to note, however, that he did not blame Beijing for having been able to get away with those practices: "I give China great credit," Trump said on a stage shared with Chinese President Xi Jinping.
"This relationship is something which we are working very hard to make a fair and reciprocal one," Trump said. "Trade between China and the United States has not been — over the last many many years — a very fair one for us."
Trump pointed to the "huge" annual trade deficit his country has with China, which he described as "a number beyond anything what anybody would understand."
"We must immediately address the unfair trade practices that drive this deficit along with barriers to market success: We really have to look at access, forced technology transfer and the theft of intellectual property — which just by itself is costing the United States and its companies at least $300 billion a year."
The president said the current relationship between the two countries is a "very one-sided and unfair one."
"But, but, I don't blame China," Trump added to scattered applause in the room. "After all, who can blame a country for being able to take advantage of another country for the benefit of its citizens? I give China great credit."
Instead, Trump laid the blame on "past administrations for allowing this out-of-control trade deficit to take place and to grow."
Trump said he is seeking to close that gap because "it just doesn't work for our great American companies and it doesn't work for our great American workers."
"It is just not sustainable," he added.
The U.S. leader's commentary was not a surprise — he has frequently identified the trade imbalance as a problem he wants to solve — but his tone is being scrutinized.
"His opening comments may be taken as slightly hostile or some taunting," said Gavin Parry, managing director at Parry International Trading. "Particularly when he mentioned the [intellectual property] aspect of cross-border loss for the U.S. side."
For his part, Xi said Thursday that China will be more open and transparent to foreign companies, including those from the United States.
U.S. companies are also welcome to take part in China's "Belt and Road" initiative, Xi told a briefing in Beijing after talks with Trump. China's door to the world will only open wider, he said.
—Reuters contributed to this report.