President Donald Trump's administration says a "phase one" deal with Beijing is imminent which would see billions of dollars of tariffs on Chinese goods removed.
Beijing aims to become the world's dominant military force, and its rapid progress took the Pentagon by surprise.
30 years later, the sad reality is that we have no strategy to change the evolution of China away from a Communist Party-controlled giant surveillance system.
The comments came just days after Xi reserved the right to use force to bring Taiwan under the mainland's control.
"We will turn to countries with similar values to fight together against China's increasingly out-of-control international behavior," Taiwan President Tsai Ing-wen said.
"We must…cast the ideological foundation of the army's absolute loyalty to the party," Xi said.
Mattis is the first Pentagon chief to visit China since 2014.
"It could very well be that he's influencing Kim Jong Un. We'll see what happens," Trump said.
China will begin applying an extension of the system to flights and trains to stop millions of people who have committed misdeeds.
The two leaders will meet for an "informal summit" just eight months after a tense military border standoff.
"The toilet issue is no small thing," Xi said. "It's an important aspect of building civilized cities and countryside."
Ri Sol Ju was seen in at least three different outfits during her two-day visit to Beijing this week.
Only two "no" votes were cast, reflecting increased efforts to stamp out opposition, Steve Tsang says.
"This is something that shakes the core of our generation; scrapping term limits definitely destroys our fantasy that we have freedom," the #NotMyPresident campaign organizer said.
Chinese authorities are cracking down on criticism of Xi Jinping's plan to stay in office for more than two terms.
"War is not far from us... China cannot afford a military failure," wrote the PLA Daily as President Xi Jinping called for the military to demonstrate heroism and a fighting spirit.
Some economists say it's just a matter of time before China overtakes the U.S. as the world's leading economy by all indicators.
China is leading the world in developing unbreakable encryption using quantum physics.