LONDON - Copper prices in London extended declines on Friday, heading for the biggest weekly loss in four weeks, driven by a strong dollar and patchy data from major economies including top metals consumer China.

Three-month copper on the London Metal Exchange (LME) was down 1% at $8,240 per metric ton in open-outcry trading. The contract is down 3.1% this week.

"Day-to-day trading of base metals prices is mainly U.S. dollar-led these days, with mixed signs of manufacturing activity performance in and outside China," said John Meyer, head of research at SP Angel in London.

The dollar fell on Friday but was still heading for its longest weekly winning streak in nine years, bolstered by a resilient run of U.S. economic data.

China's onshore yuan, meanwhile, dropped to its lowest weakest since 2007, making dollar-priced metals less attractive for Chinese investors.

Citing a softer copper demand outlook from China and increase in exchange stocks, Commerzbank cut its year-end target copper price on Friday to $8,800 a ton from $9,000.

Copper stocks in warehouses registered with the Shanghai Futures Exchange rose 18% from a week ago, exchange data released on Friday shows. Total inventory stood at 54,955 tons.

In other metals, LME aluminium shed 0.7% to $2,180 a ton, nickel dropped 1.9% to $20,100, zinc fell 2% to $2,429.5, lead was down 0.6% at $2,217 and tin retreated by 1.9% to $25,600.

(Reporting by Julian Luk in London; Editing by David Goodman)