"China hopes to see a prosperous Europe, a united European Union," Xi was paraphrased as saying to Cameron during talks on Thursday in a statement issued during his visit to Britain on today.
"China hopes Britain will be an important member country of the European Union to be a more positive and constructive element to deepen the development of Sino-European relations," the statement said.
Contacted by AFP, Cameron's office declined to comment.
Cameron has said he will support Britain remaining in the EU in a referendum due to be held by 2017 but only if he manages to negotiate a series of reforms that would increase Britain's powers.
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He has not ruled out advocating leaving the 28-country bloc.
The prime minister faces pressure from Eurosceptics inside his own Conservative Party as well as the anti-EU UK Independence Party (UKIP) and opinion polls indicate the referendum could be a close vote.