Chinese foreign ministry spokesman Lu Kang said a one-day extension in talks showed both sides are serious about the talks.
The global economy has been suffering from the chilling effect of a trade war between the world's two largest economies.
The two sides will keep in close contact, it added.
China and the U.S. plan to release a message on trade talks at the same time Thursday morning in Beijing, he said later in another tweet.
No schedule for further face-to-face negotiations was released, and USTR said the American delegation would return to Washington to report on the meetings and "to receive guidance on the next steps". US President Donald Trump tweeted that they were "going really well!"
Later this month, US Trade Representative Robert Lighthizer is expected to meet with Vice Premier Liu He, President Xi Jinping's top economic aide who is leading negotiations for China, a person familiar with the situation said last week.
The talks also focused on "China's pledge to purchase a substantial amount of agricultural, energy, manufactured goods, and other products and services from the US" according to the USTR.
China is keen to put an end to its trade dispute with the United States but will not make any "unreasonable concessions" and any agreement must involve compromise on both sides, the China Daily, a state newspaper, said on Wednesday. Without a breakthrough in talks, USA corporations are likely to experience a deepening decline in their Chinese sales, with Bank of America Merrill Lynch analysts even seeing an "informal boycott" in place.
The midlevel talks in Beijing concluded on Wednesday.
As evidence mounts by the day that the slowdown in China's economy is worsening, policy makers in Beijing are focusing on getting rid of the duties that Trump has leveled on Chinese goods since a year ago, according to a former high-level official briefed on the government's thinking. Trump has complained repeatedly about the USA trade deficit with China, which previous year likely exceeded the 2017 gap of $336 billion.
The United States has long complained about access to the vast Chinese market and Beijing's demands USA companies reveal their technology advances.
The US president is increasingly eager to strike a deal with China soon in an effort to perk up financial markets that have slumped on concerns over the trade war, according to people familiar with internal White House deliberations. USA officials appear to want to maintain the pressure of tariffs, the official said. This meeting was previously unscheduled, signaling the two sides could be coming together on key issues.
"The U.S. feels uncomfortable with China's rapid development, and can't adapt to its own declining influence", wrote Chen Yonglong in the state-run China Daily".
Trump imposed tariff increases of up to 25 percent on $250 billion of Chinese imports.
Trump and Xi have given their officials until March 1 to reach an accord on "structural changes" to China's economy on issues such as the forced transfer of American technology, intellectual-property rights, and non-tariff barriers.