PARIS (Reuters) - PSA Group's <PEUP.PA> first-half sales fell 0.2 percent, the French carmaker said on Tuesday, citing difficulties in a weaker, "westernising" Chinese market that obscured a stronger performance at home in Europe.

The European market is likely to see a slight decline following Britain's June 23 referendum vote to leave the European Union, the company also cautioned.

Deliveries of Peugeot, Citroen and DS cars declined to 1.54 million vehicles, falling behind domestic rival Renault <RENA.PA> in January-June, as sales in China and Southeast Asia slumped almost 20 percent.

"In China we're in the process of adapting to a fast-changing market that is westernising and no longer in rapid growth," the group's Europe chief Denis Martin told reporters on a call.

Chinese mid-market consumers are gravitating to competitively priced SUVs built by domestic carmakers, putting pressure on western brands. PSA plans to defend its corner with an imminent product offensive that includes five four-by-four offerings.

In Europe, PSA's sales rose 7.4 percent, led by the Peugeot 2008 mini-SUV and Partner delivery van.

Martin said the European market may suffer a "slight slowdown" in the second half following Britain's June 23 referendum vote to leave the European Union. But he maintained the company's 4 percent growth forecast for the full year.

(Reporting by Laurence Frost and Gilles Guillaume; Editing by Andrew Callus)