The queen made the comments while talking to Metropolitan Police commander Lucy D'Orsi during a garden party at Buckingham Palace on Tuesday.
After D'Orsi was introduced as the officer in charge of security during the Chinese visit, the queen replied: "Oh, bad luck."
The Queen has been caught calling Chinese officials "very rude" on camera and saying "bad luck" to their escorthttps://t.co/DFsZFoPSCU— RT UK (@RTUKnews) 11 May 2016
The 90-year-old monarch was later heard saying:
"They [Chinese officials] were very rude to the ambassador," referring to behavior directed towards the British ambassador to China, Barbara Woodward.
D'Orsi told the queen that President Xi's visit had been "quite a testing time for me," claiming that Chinese officials had "walked out" on her and the ambassador, telling them "that the trip was off."
The queen and D'Orsi were accompanied by another official, who said police had been "seriously undermined by the Chinese" during the visit.
Police commander D'Orsi concluded the conversation by saying:
"It's very rude and very undiplomatic, I thought."
Questions Raised Over 'Golden Era'
The embarrassing gaffe has also raised questions about the future of the much-touted "golden era" of relations between Britain and China.
Speaking in Beijing, Chinese Foreign Ministry spokesperson Lu Kang, declined to comment on whether the queen's comments and the state of UK-Chinese relations.
"President Xi's visit to the UK last year was a very successful one. Both sides have made great efforts for the success of the visit and the two sides highly recognized that," Lu was quoted as saying by the Guardian.
When questioned further whether the "golden era" was still alive, he replied: "Both sides have expressed the hope that they would implement the outcomes of President Xi's visit and push forwards a steady and stable rise of the bilateral relationship. This requires the common efforts of both sides."
Looking to play down the embarrassing leak, a Buckingham Palace spokesperson said:
"We do not comment on the Queen's private conversations. However, the Chinese State Visit was extremely successful and all parties worked closely to ensure it proceeded smoothly."
Cameron's 'Fantastically Corrupt' Slip
The embarrassing diplomatic gaffe was the second involving the monarch in as many days after UK Prime Minister David Cameron was overheard describing Nigeria and Afghanistan as "fantastically corrupt" ahead of London's anti-corruption summit this week.
Cameron told the Queen: "We had a very successful Cabinet meeting this morning to talk about our anti-corruption summit. We've got the Nigerians… actually we've got the leaders of some fantastically corrupt countries coming to Britain".
"Nigeria and Afghanistan, possibly the two most corrupt countries in the world."
The comments triggered a sharp response from Nigerian President Muhammadu Buhari, who called for the "return of assets" from the UK to Nigeria.
"What do I need an apology for? I need something tangible," Buhari said during his keynote speech at the opening of a Commonwealth anti-corruption summit being held in London.
"I’m not going to demand any apologies from anybody, what I’m demanding is a return of assets."
Buhari has made the fight against corruption one of his big since becoming president last year.