LONDON, Jan 25 (Reuters) - WPP, the world's biggest advertising group, said it would merge its two largest communications agencies Hill & Knowlton and BCW, in the latest internal tie-up aimed at driving efficiencies within the company.

London-based WPP, which owns creative agencies such as Ogilvy and media planner GroupM, said on Thursday that the combined group would be renamed Burson and have 6,000 staff in 43 markets, adding that there were synergies between the units.

WPP is battling to eke out growth after tech clients reined in spending on marketing last year and amid tough conditions in China. It cut its outlook in October, forecasting like-for-like growth of 0.5-1.0% in 2023, down from previous guidance of 1.5-3.0%.

The merger announced on Thursday follows plans announced three months ago to merge its two major creative agencies, Wunderman Thompson and VMLY&R.

WPP chief executive Mark Read said Burson would be an industry-leading, full-service communications agency.

"Hill & Knowlton and BCW are two high-performing businesses with complementary strengths, shared ambitions and many shared clients," he said.

Corey duBrowa, currently BCW's CEO, was named global CEO of Burson, and AnnaMaria DeSalva, Hill & Knowlton's CEO, will be chair of the new group. Burson would be operational by July 1, the statement added.

Shares in WPP, which have lost 18% of their value over the last 12 months, were up 1% at 763 pence in afternoon trading outperforming Britain's bluechip market which was flat. (Reporting by Sarah Young; editing by William James)