Donald Trump and China's President Xi Jinping at a dinner meeting in Buenos Aires, on Saturday. (AFP)

The United States said Saturday that it agreed in a long-awaited summit with China to suspend new tariffs for 90 days as the two powers seek to end a trade war. The White House said a threatened increase of tariffs on $200 billion worth of Chinese goods from 10 to 25 percent, which was set to take effect on January 1, would be put off for 90 days.

"If at the end of this period of time, the parties are unable to reach an agreement, the 10 percent tariffs will be raised to 25 percent," a White House statement said after dinner talks between President Donald Trump and his counterpart Xi Jinping on the sidelines of a G20 summit in Buenos Aires.

Trump, who in recent months has harshly criticized China and accused it of meddling in US elections, in the statement called his meeting with Xi "amazing and productive."

China earlier confirmed the outlines of the arrangement, saying that officials of the world's two largest economies would get to work on resolving a range of trade disputes.

The White House said that China has also agreed to step up purchases "immediately" of an unspecified amount of US agricultural goods.

Amid the trade tensions, China has sharply curtailed its purchases of US soybeans and other produce, dealing a significant blow to farmers, a major support base for Trump.

In what the White House called a "wonderful humanitarian gesture," the White House said that Xi would crack down on fentanyl, the opioid painkiller largely made in China that is behind an epidemic of US overdoses.

The White House said that China would subject fentanyl makers to the "maximum penalty under the law." China is the world's leading executioner, with drug offenses subject to the death penalty.