Britain's Prime Minister David Cameron (right) walks in the gardens as he welcomes Chinese President Xi Jinping, with an interpreter (obscured), to his official residence at Chequers, England, Oct. 22, 2015. Reuters/Kirsty Wigglesworth/Pool

BEIJING (Reuters) - China hopes to see a united European Union in which Britain plays a prominent role in promoting Chinese relations with the bloc, President Xi Jinping told Britain's prime minister, making in an indirect plea for the country to remain part of the EU.

Prime Minister David Cameron is seeking to renegotiate Britain's relationship with the EU, which it joined in 1973, as the 'in' and 'out' campaigns prepare for battle in a referendum on membership which will be held before 2017.

China typically does not comment on votes in other countries, viewing it as an interference in an internal affair.

But Beijing has been worried about the implications of free trade-supporting Britain leaving the EU, and of any weakening of a grouping which it views as a vital counterbalance to the United States, diplomats say.

Meeting at the prime minister's official country residence at Chequers late Thursday, Xi told Cameron the EU is a strategic partner of China's and also its largest trading partner, China's foreign ministry said in a statement released on Friday.

"China hopes to see a prosperous Europe and a united EU, and hopes Britain, as an important member of the EU, can play an even more positive and constructive role in promoting the deepening development of China-EU ties," it paraphrased Xi as saying.

There was no direct mention of the British vote on whether to leave the EU.

China's Foreign Ministry made similar comments before Xi left.

Xi is on his first state visit to Britain, 10 years after the last such trip by a Chinese president.

The British government has moved forcefully to strengthen financial and political ties with Beijing. Earlier this year, it broke ranks with the United States by signing up as a founding member of China's new infrastructure investment bank.