LONDON – Another surge in copper stockpiles tracked by the world’s top base-metals bourse is reigniting concerns about demand for the material that’s often viewed by investors as a bellwether for the global economy.

A 40% jump in inventories monitored by the London Metal Exchange in just three days comes amid concerns about China’s slowing industrial activity. Prices of copper, referred to as the metal with a Ph.D in economics, are trading near a four-month low.

Financial markets in China, the top copper user, are feeling the pressure of tighter liquidity and rising money-market rates that have pushed down prices of iron ore to zinc. Investors are also waiting for US President Donald Trump to push through electoral pledges, including boosting stimulus spending that helped push copper prices higher since late last year.

“The optimism over Trump’s spending and China has been overblown,” Dan Smith, head of commodities research at Oxford Economics in London, said by phone.

While copper futures were little changed on the LME Friday, they’re heading for the biggest weekly drop this year.

Copper held in LME warehouses climbed more than 11% for a third day and is at the highest since October. A measure of stockpiles tracked by the LME, Comex and Shanghai Futures Exchange rose 13% this week.

Still, analysts said the LME inflows could also be due to traders moving metal from China to other destinations to profit from a price gap between LME and Shanghai prices. The London bourse doesn’t have any storage facilities in China.

“Some are saying it could be a reflection of weak demand in China, but equally it could simply be that stocks are being relocated from the Shanghai Futures Exchange to London Metal Exchange warehouses due to the arbitrage,” Robin Bhar, an analyst at Societe Generale SA in London, said by phone. “That would be my favored theory.”

Recent history shows the LME’s incoming metal may be in strong demand. Three similarly large inflows since August were then withdrawn in the following months.

“The pattern has been one of volatility, with stocks increasing sharply and then falling away,” Eugen Weinberg, an analyst at Commerzbank AG in Frankfurt, said by phone. “It’s a massive inflow, but whether we will see outflows in the next few weeks remains to be seen.”