Keir Starmer has arrived in Beijing as he begins the first British prime ministerial visit to China since 2018.
On the plane to China, Starmer said the UK cannot afford to ignore the economic opportunities presented by China, the world's second-largest economy, while it must remain vigilant about potential security threats.
"It doesn't make sense to stick our head in the ground and bury it in the sand when it comes to China, it's in our interests to engage," he said.
"It's going to be a really important trip for us and we'll make some real progress."
Travelling with a delegation of more than 50 business leaders, Starmer will meet with President Xi Jinping and Premier Li Qiang on Thursday before travelling to Shanghai on Friday for talks with local executives.
The visit could mark a critical shift in ties between Britain and China after years of deep acrimony over Beijing's crackdown on political freedoms in Hong Kong, China's support for Russia in the Ukraine war and allegations by British security services that China regularly spies on politicians and officials.
For China, the visit offers the country a chance to portray itself as a stable and reliable partner at a time of global disorder.
The trip comes at a time when there is a flurry of diplomacy between Western countries and China as they hedge against the unpredictability of the US.
Starmer's trip follows weeks of tensions with Trump over his threats to seize Greenland, his criticism of Britain's deal to cede sovereignty of the Chagos Archipelago - including an island with an important US-UK air base - to Mauritius, and his comments that NATO allies avoided front-line combat during the war in Afghanistan.
Starmer was reluctant to be drawn on what he would discuss with Chinese leaders, or if he would bring up the fate of Jimmy Lai, the former Hong Kong media tycoon who was convicted in December of national security crimes. He also declined to say whether he would ask China to pressure Russia to end the Ukraine war.
Asked if Britain and China could strike a deal that would allow more visa-free travel, Starmer said he hoped to make some "progress" in that area.
Starmer repeatedly defended his decision to visit China, saying it would help him deliver on his plan to drive economic growth and improve living standards in Britain.
But his strategy has drawn fierce criticism from some British and US politicians who say he is underestimating the security threats posed by China.
with Reuters