The 20,000-square-metre site is set to become the largest embassy complex in the UK by area and one of the largest in the centre of a Western capital.
China said on Wednesday that the United Kingdom had an "obligation" to approve its new mega embassy in London, a day after the controversial plans were given the green light.
"Providing support and convenience for the construction of diplomatic premises is an international obligation of the host country," foreign ministry spokesperson Guo Jiakun said at a news conference.
The 20,000-square-metre site is set to become the largest embassy complex in the UK by area and one of the largest in the centre of a Western capital.
The UK approved its construction on Tuesday.
Plans for the embassy have been plagued by objections and protests since 2018, when China's government bought the site at Royal Mint Court, near the Tower of London, for £225 million (€259 million).
It triggered anger and protests from rights groups and activists, who fear the site could be used to spy on and harass dissidents.
Opponents also say the huge site sits too close to underground fibre optic cables carrying sensitive financial information between London’s two main financial districts.
While British housing minister Steve Reed said the decision was final, it could still face legal challenges, with residents in London vowing to act.
Ties between China and Britain plummeted under the previous Conservative government, with the new embassy appearing to be a sticking point.
China had complained about the seven-year delay in approving the project, saying that the UK was "constantly complicating and politicising the matter."
British Prime Minister Keir Starmer, whose Labour party swept to power in 2024 elections, has sought to reset ties with the economic powerhouse and will reportedly visit China later this month.
While the embassy approval could boost relations, security minister Dan Jarvis noted that China would still continue to pose national security threats to Britain.