US President Donald Trump took to Twitter Tuesday to slam China, just as US negotiators arrived in Shanghai to resurrect stalled trade talks with Chinese officials.

"My team is negotiating with them now, but they always change the deal in the end to their benefit," Trump tweeted.

"China is doing very badly, the worst year in 27 - was supposed to start buying our agricultural product now - no signs that they are doing so. That is the problem with China, they just don't come through."

The negotiations are the first face-to-face talks since Trump agreed to a truce with Chinese President Xi Jinping at June's G20 summit, Washington and Beijing have so far hit each other with punitive tariffs covering more than $360 billion in two-way trade.