Donald Trump boasts about 'beautiful letter' from Chinese President Xi Jinping

US President Donald Trump says he had received a "beautiful letter" from Chinese President Xi Jinping as negotiations on a trade deal between the two countries continue in Washington.

"He just wrote me a beautiful letter. I've just received it and I'll probably speak to him by phone," Trump said on Thursday.

Later he quoted Xi as saying in the letter: "Let's work together, let's see if we can get something done".

Trump said he believed it was possible to reach a deal this week, as negotiators prepare to meet again on Thursday in Washington to end a trade dispute between the world's two largest economies.

The US Trade Representative's office announced that tariffs on US$200 billion (NZ$303 billion) worth of Chinese goods would increase to 25 percent from 10 percent at 12:01am (local time) on Friday, right in the middle of two days of meetings with a Chinese delegation.

Trump has accused China of reneging on commitments it had made so far in the talks.

"We're getting very close to a deal, then they started to renegotiate the deal. We can't have that. We can't have that," he said.