Watch: Trump arrives in China amid North Korea tensions

US President Donald Trump toured the Forbidden City with Chinese leader Xi Jinping on Wednesday as he began the crucial leg of an Asian tour intended to build a global front against North Korea's nuclear threats.

After warning North Korea's "cruel dictatorship" against testing the United States during a speech in Seoul, Trump and First Lady Melania Trump were met by Xi and his wife Peng Liyuan for tea at the former imperial palace.

But the genial gathering will be followed on Thursday by a full day of thorny talks, with Trump looking to prod Xi into doing more to squeeze North Korea economically and to address China's massive trade surplus with the United States.

The Trump administration sees Beijing as the key to controlling Pyongyang, which depends on China for its economic survival and for 90 percent of its trade.

Earlier, Trump congratulated Xi on his reappointment as China's Communist Party chief, tweeting: "I very much look forward to meeting with President Xi who is just off his great political victory."

Trump's use of the term "political victory" for the outcome of last month's Communist Party congress was seen by analysts as an attempt to conciliate Xi before tough talks on trade and North Korea.

"He's laying it on thick to put Xi in a good mood because he will have unpleasant things to tell him," said Jean-Pierre Cabestan, China politics specialist at Hong Kong Baptist University.

Xi has prepared an extravagant "state visit-plus" for Trump, with opera and a lavish banquet, and the US leader has brought a business delegation along for the ride. Deals are expected to be signed, though they may not be enough to allay US concerns about China's massive trade surplus, which narrowed in October but remained high at a monthly $26.6 billion.