Trump made the remarks to reporters while attending the premiere of a documentary about his wife, First Lady Melania Trump.

Asked on the press line for his reaction to Britain "getting into business" with China, the president said: "Well it's very dangerous for them to do that."

Starmer's visit to China is the first by a British premier since 2018 and follows a slew of Western leaders seeking a rapprochement with Beijing recently, seen by many as a pivot from an increasingly unpredictable United States.

On Thursday, Starmer met with Xi and other Chinese officials, and signed several cooperation agreements.

Canadian Prime Minister Mark Carney also visited China in mid-January and reached agreements on trade and tourism.

Afterward, Trump threatened to hit Canadian imports with 100-percent tariffs if Carney made further deals with Beijing -- a threat the Canadian PM later dismissed as a negotiating tactic.

Trump, after remarking Thursday on Britain, added: "It's even more dangerous, I think, for Canada to get into business with China. Canada is not doing well. They're doing very poorly, and you can't look at China as the answer."