Copper prices extended their fall to a seventh consecutive session on Tuesday to hit their lowest in three and a half months on growing concern over demand in top consumer China.

Three-month copper on the London Metal Exchange (LME) dropped 0.6% to $9,165 a metric ton in official open-outcry trading after hitting $9,115 for its lowest since April 3.

"Chinese demand is soft, which has been the case for a while," said Dan Smith, head of research at Amalgamated Metal Trading.

"Two factors triggered lower prices. One is disappointment about the Chinese (Communist Party's) third plenum, as there was hope that it would lift the market."

He also pointed to algorithmic computer trading models, saying they had started triggering a sell signal.

Last week's plenum, a key political meeting, failed to lay out more policies to prop up demand for metals. Chinese shares registered their biggest one-day drop in six months on Tuesday.

Against a backdrop of subdued domestic consumption, Chinese copper producers shipped out a record 157,751 tons last month, contributing to higher inventories in LME-registered warehouses, weighing on prices.

LME copper stocks grew to 236,700 tons, LME data shows. That is the highest since September 2021, boosted by delivery of 2,350 tons to two Asian warehouses close to China.

The surplus in the global refined copper market widened to 416,000 tons in the January to May period, from 154,000 tons in the same period last year, according to the International Copper Study Group.

Other base metals were also down, though aluminium was an exception with buying spurred by prices that hit the lowest since March 28 on Monday. Aluminium was up 0.7% at $2,315 a ton in official activity.

LME zinc lost 1.1% to $2,697 a ton, tin dropped 2.6% to $29,100 and nickel was down 0.9% at $16,050.

Lead slipped by 0.5% to $2,073.5. Large amounts of lead were delivered to LME warehouses in Singapore on Monday for profitable financial deals, taking total stocks of the battery metal to their highest since early May.

(Reporting by Polina Devitt Additional reporting by Siyi Liu Editing by David Goodman)